@article{abdelhamid_routh_hagar_bedair_2022, title={Improved LED output power and external quantum efficiency using InGaN templates}, volume={120}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0084273}, DOI={10.1063/5.0084273}, abstractNote={InGaN templates have recently attracted interest due to their ability to reduce strain in the quantum wells and to induce a red shift in the emission wavelength. For such technology to be competitive, it should outperform the traditional technology for LEDs grown on GaN substrates and offer improved output characteristics. InGaN based LEDs on In y Ga 1−y N templates with varying In-content of 8% ≤ y ≤ 12% are studied for the same emission wavelength. The electroluminescence, optical output power, and external quantum efficiency of the LEDs are investigated as a function of the In-content in the templates. LEDs on InGaN templates with In-content of 8–10% show better performance than LEDs grown on GaN. This enhancement is attributed to improved radiative recombination as a result of the reduced strain in the quantum wells. However, templates with In-content of ∼10.5% and ∼11% show inferior performance to the LEDs on GaN because the deterioration from the increased defects from the template is stronger than the improvement in the radiative recombination. It can be concluded that the InGaN templates with 8–10% offer a technology for LEDs that is outperforming the traditional GaN technology.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Abdelhamid, Mostafa and Routh, Evyn L. and Hagar, Brandon and Bedair, S. M.}, year={2022}, month={Feb} }
 @article{hagar_abdelhamid_routh_colter_bedair_2022, title={Ohmic co-doped GaN/InGaN tunneling diode grown by MOCVD}, volume={121}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0103152}, DOI={10.1063/5.0103152}, abstractNote={Tunnel junctions (TJs) have recently been proposed as a solution for several III-nitride current problems and to enhance new structures. Reported III-nitride TJs grown by metalorganic chemical vapor deposition (MOCVD) resulted in backward diodes with rectifying behavior in forward bias, even with Mg and Si doping in 1020 cm−3. This behavior limits applications in several device structures. We report a TJ structure based on p+In0.15Ga0.85N/n+In0.05Ga0.95N, where the n-side of the junction is co-doped with Si and Mg and with electron and hole concentrations in the mid-1019 cm−3 for both the n and p dopants. Co-doping creates deep levels within the bandgap that enhances tunneling under forward biased conditions. The TJ structure was investigated on both GaN substrates and InGaN templates to study the impact of strain on the TJ I–V characteristics. The resulting TJ I–V and resistivities reported indicate the potential for this TJ approach in several device structures based on III-nitrides. We are not aware of any previous MOCVD grown TJs that show Ohmic performance in both forward and reverse biases.}, number={5}, journal={APPLIED PHYSICS LETTERS}, author={Hagar, B. G. and Abdelhamid, M. and Routh, E. L. and Colter, P. C. and Bedair, S. M.}, year={2022}, month={Aug} }
 @article{routh_abdelhamid_colter_el-masry_bedair_2021, title={P-type InxGa1-xN semibulk templates (0.02 < x < 0.16) with room temperature hole concentration of mid-10(19) cm(-3) and device quality surface morphology}, volume={119}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0065194}, DOI={10.1063/5.0065194}, abstractNote={Using the semibulk approach, p-InxGa1−xN semibulk (p-SB) templates were grown with an indium content ranging from 2.4% to 15.2% via metalorganic chemical vapor deposition. When compared to optimized bulk p-GaN, the hole concentration in p-SB with an In content of ∼15.2% increased by two orders of magnitude from 5.22 × 1017 to 5.28 × 1019 cm−3. The resistivity and mobility of the templates decreased gradually from 3.13 Ω · cm and 3.82 cm2/V s for p-GaN to 0.24 Ω · cm and 0.48 cm2/V s for p-SB with an In content of 15.2%. Temperature dependent Hall measurements were conducted to estimate the activation energy of the p-SB template. The p-SB with the In content of ∼15.2% is estimated to have an activation energy of 29 meV. These heavily doped p-SB templates have comparable material qualities to that of GaN. The atomic force microscopy height retraces of p-SB films show device quality surface morphology, with root mean square roughness ranging from 2.53 to 4.84 nm. The current results can impact the performances of several nitride-based devices, such as laser diodes, LEDs, solar cells, and photodetectors.}, number={12}, journal={APPLIED PHYSICS LETTERS}, author={Routh, Evyn L. and Abdelhamid, Mostafa and Colter, Peter and El-Masry, N. A. and Bedair, S. M.}, year={2021}, month={Sep} }
 @article{abdelhamid_routh_shaker_bedair_2021, title={Shifting LED emission from blue to the green gap spectral range using In0.12Ga0.88N relaxed templates}, volume={160}, ISSN={["1096-3677"]}, url={https://doi.org/10.1016/j.spmi.2021.107065}, DOI={10.1016/j.spmi.2021.107065}, abstractNote={InyGa1-yN templates are grown with y ≤ 13.5% and a few nm surface roughness. These templates are used successfully to address two of the main issues facing long wavelength emitting LEDs, mainly the low growth temperature and high values of strain in the quantum wells (QWs). In this work, three LED structures are investigated: the first is a blue LED grown on GaN, the second and third are green LEDs grown on relaxed InyGa1-yN templates with y of about 10% and 12%, respectively. The same multiple quantum wells (MQWs) were used in the three LED structures, with the same well width, barrier width, and growth temperature. The reduced strain in the QWs due to the use of InGaN templates enhances the indium incorporation rate in the QWs. Red shift in emission wavelength of about 100 nm, from 470 nm to 570 nm, was achieved, at low injection current. Optical output power and external quantum efficiency (EQE) measurements showed that at high level of current injection, performance of the blue LED is about twice of the green emitting LEDs on InGaN templates. The current results indicate the potential of the InGaN template approach, with high values of y, in addressing problems facing long wavelength InGaN LEDs.}, journal={SUPERLATTICES AND MICROSTRUCTURES}, author={Abdelhamid, Mostafa and Routh, Evyn L. and Shaker, Ahmed and Bedair, S. M.}, year={2021}, month={Dec} }
 @article{abdelhamid_routh_bedair_2021, title={The dependence of the emission from MQWs on the indium content in the underlying InGaN templates: experimental and modeling results}, volume={36}, ISSN={["1361-6641"]}, DOI={10.1088/1361-6641/abe141}, abstractNote={Abstract The effect of underlying highly relaxed In y Ga 1- y N templates on In x Ga 1- x N multiple quantum wells (MQWs), where x > y , is investigated. Photoluminescence (PL) measurements and tested light emitting diodes (LEDs) show that relaxed In y Ga 1- y N templates with y ∼ 10% can cause a red shift in MQWs emission of <?CDATA ${{\Delta }}E\sim 0.33{\textrm{eV}}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> </mml:mrow> <mml:mi>E</mml:mi> <mml:mo>∼</mml:mo> <mml:mn>0.33</mml:mn> <mml:mrow> <mml:mrow> <mml:mtext>eV</mml:mtext> </mml:mrow> </mml:mrow> </mml:math> . This red shift is attributed to the reduced strain in the MQWs, resulting in a decrease in the MQWs band gap, along with an increase in indium incorporation in the QWs due to composition pulling effect. Theoretical modeling was applied to study the effect of the template’s indium content and its degree of relaxation on the observed red shift in MQW emission. The proposed model uses the PL emission data from the MQW to predict the indium content in the MQWs grown on GaN and on InGaN templates. Using this model, we are able to predict the dependence of both the amount of the red shift and the indium incorporation enhancement in the QWs on the In-content in the underlying templates. We are not aware of any similar modeling activities that reported such predictions. LED devices were fabricated using the In y Ga 1- y N templates and compared to conventional LED structure grown on GaN, showing a red shift in electroluminescence that agrees with the PL results.}, number={3}, journal={SEMICONDUCTOR SCIENCE AND TECHNOLOGY}, author={Abdelhamid, Mostafa and Routh, Evyn L. and Bedair, S. M.}, year={2021}, month={Mar} }
 @article{khafagy_hatem_bedair_2021, title={Thermodynamics Models for V-pit Nucleation and Growth in III-Nitride on Silicon}, volume={73}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-020-04421-z}, number={1}, journal={JOM}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2021}, month={Jan}, pages={293–298} }
 @article{routh_abdelhamid_el-masry_bedair_2020, title={Device quality templates of InxGa1-xN (x < 0.1) with defect densities comparable to GaN}, volume={117}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0015419}, DOI={10.1063/5.0015419}, abstractNote={InGaN/GaN multiple quantum well (MQW) structures currently used in optical devices are based on highly strained InGaN films. The presence of strain reduces quantum efficiency and indium incorporation, two critical parameters in addressing the green gap. We report on the growth of InGaN-relaxed templates on GaN as substrates to reduce the strain in the MQW structures. Relaxation in the InGaN templates, due to the lattice mismatch, is accommodated by the generation of V-pits rather than the formation of misfit dislocations. InxGa1−xN templates (x ∼ 0.1) are grown via a modified semibulk (SB) approach, with a gradually increasing GaN interlayer thickness to provide a mechanism for backfilling of V-pits. We used high-resolution x-ray diffraction rocking curves to quantify the edge-type and screw-type dislocation density present in the SB and compared the results with the etch pit density obtained via atomic force microscopy after treating the SB with a silane etch. Device-quality InGaN templates with defect density in the mid 108 cm−2 were investigated using the above two approaches, with a quality comparable to state-of-the-art GaN.}, number={5}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Routh, Evyn L. and Abdelhamid, Mostafa and El-Masry, N. A. and Bedair, S. M.}, year={2020}, month={Aug} }
 @article{khafagy_hatem_bedair_2020, title={Dislocation-Based Thermodynamic Models of V-Pits Formation and Strain Relaxation in InGaN/GaN Epilayers on Si Substrates}, ISBN={["978-3-030-36295-9"]}, ISSN={["2367-1696"]}, DOI={10.1007/978-3-030-36296-6_188}, abstractNote={The strain relaxation mechanism in III-N materials is occurred through the motion of dislocations that generated at III-N/Si interface as a result of large mismatch in lattice and thermal expansion coefficients. As a result of the large lattice mismatch between different layers, the upper layer gets strained and with thicker layers, the strain energy increases until a thickness limit called the critical material thickness. Most of such dislocations (threading dislocations) penetrate the top surface forming V-pits defects at the top surface that relax the material. These V-pits directly affect the device efficiency, performance, and reliability. Therefore, in this paper, a thermodynamics-based model will be used to study the V-pits formulation and growth in the III-N (especially, InGaN-based materials). In this model, three types of energies are used under a balanced system to model the V-pit formation and growth. These energies are the strain energy in the InGaN epilayer, the destruction energy as a result of dislocation to form the V-pit, and the strain energy of the V-pits facets that generated during the facet nucleation.}, journal={TMS 2020 149TH ANNUAL MEETING & EXHIBITION SUPPLEMENTAL PROCEEDINGS}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2020}, pages={2057–2064} }
 @article{hagar_sayed_colter_bedair_2020, title={Multi-junction solar cells by Intermetallic Bonding and interconnect of Dissimilar Materials: GaAs/Si}, volume={215}, ISSN={["1879-3398"]}, DOI={10.1016/j.solmat.2020.110653}, abstractNote={Abstract We present a novel, low temperature approach to multijunction solar cell fabrication combining the high efficiency multi-junction concept with the low cost of thin film technology in one solar cell structure. The intermetallic bonding approach presented is based on joining indium metal which has been deposited on the metal contact grid of the respective solar cells. This approach avoids the problems of lattice mismatch and tunnel junction limitations, connecting solar cells of potentially any material with patterned contacts. No measurable increase in resistance has been measured between bonded materials. This method allows the independent development of each cell technology for use in multijunction solar cells. This technique can be applied to any commercial off-the-shelf solar cells, if available. A GaAs/Si multijunction solar cell bonded using this approach is demonstrated. The silicon cell is off-the-shelf with textured surface and commercial metal contacts. This is integrated with an in-house grown thin film GaAs cell. The GaAs/Si device is demonstrated in both two and three terminal configurations.}, journal={SOLAR ENERGY MATERIALS AND SOLAR CELLS}, author={Hagar, Brandon and Sayed, Islam and Colter, Peter C. and Bedair, S. M.}, year={2020}, month={Sep} }
 @article{eldred_abdelhamid_reynolds_el-masry_lebeau_bedair_2020, title={Observing relaxation in device quality InGaN templates by TEM techniques}, volume={116}, ISSN={["1077-3118"]}, DOI={10.1063/1.5139269}, abstractNote={Device quality InGaN templates are synthesized using the semibulk (SB) approach. The approach maintains the film's 2D growth and avoids the formation of indium-metal inclusions. The strain relaxation processes of the grown InxGa1−xN templates are accompanied by variations in the indium content (x) and lattice parameters (a and c) across the InGaN template's thickness as the residual strain is continuously decreasing. This strain and lattice parameters' variation creates difficulties in applying standard x-ray Diffraction (XRD) and Reciprocal Space mapping (RSM) techniques to estimate the residual strain and the degree of the elastic strain relaxation. We used high-resolution High-angle annular dark-field scanning transmission electron microscopy and Energy-dispersive x-ray spectroscopy (EDS) to monitor the variations of the indium content, lattice parameters, and strain relaxation across the growing InxGa1−xN templates. We show that strain relaxation takes place by V-pit defect formation. Some of these V-pits are refilled by the GaN interlayers in the InxGa1−xN SB templates, while others propagate to the template surface. We present an alternative approach combining photoluminescence (PL) and EDS for estimating the degree of strain relaxation in these InxGa1−xN templates. The values obtained for the degree of relaxation estimated from TEM studies and PL measurements are within reasonable agreement in this study. Device quality InxGa1−xN templates with x ∼ 0.08, with a degree of relaxation higher than 70%, are achieved.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Eldred, Tim B. and Abdelhamid, Mostafa and Reynolds, J. G. and El-Masry, N. A. and LeBeau, James M. and Bedair, S. M.}, year={2020}, month={Mar} }
 @article{salah_hatem_khalil_bedair_2019, title={Embedded void approach effects on intrinsic stresses in laterally grown GaN-on-Si substrate}, volume={242}, ISSN={["1873-4944"]}, DOI={10.1016/j.mseb.2019.02.016}, abstractNote={Abstract Laterally grown GaN-on-Si substrate is promising for solid state lighting, high power density devices, and wireless communication applications among others. Despite their superior optical and electrical properties, they suffer from high dislocation-densities due to high lattice and thermal expansion coefficients mismatch between both crystalline materials. Different approaches have been suggested to reduce defects in GaN-on-Si technology. One of these approaches is Embedded Void Approach (EVA), which has been employed to control defects mobility in GaN thin-film on Si substrate by inserting micro-voids near the interface. In the current study, a three-dimensional multiple-slip crystal plasticity model and specialized finite-element formulations were used to address GaN growth on Si substrate. Furthermore, EVA has been studied to understand the effectiveness of the experimentally developed approach in reducing defects mobility. Additionally, a parametric study has been conducted to examine the effect of voids size and aspect ratio on the intrinsic stresses. It was found that EVA results in considerable reduction in the stresses in the mid surface of the structure near the voids and consequently the dislocation density at the top surface, enhancing the performance of the proposed system.}, journal={MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS}, author={Salah, Salma I. and Hatem, Tarek M. and Khalil, Essam E. and Bedair, Salah M.}, year={2019}, month={Mar}, pages={104–110} }
 @article{abdelhamid_reynolds_el-masry_bedair_2019, title={Growth and characterization of InxGa1-xN (0 < x < 0.16) templates for controlled emissions from MQW}, volume={520}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2019.05.019}, abstractNote={InxGa1−xN (0 < x < 0.16) templates were grown by Metal Organic Chemical Vapor Deposition (MOCVD) using the semibulk (SB) growth approach. We have studied the impact of different SB design parameters such as the number of (InGaN/GaN) periods, InGaN layer thickness (T), and the GaN substrate quality on the SB-template properties, and its degree of relaxation. SIMS characterization measured the variation of indium content (x) in the template, while photoluminescence reflected the indium content at the topmost layers of the SB template. X-ray diffraction techniques measured the average lattice parameters and degree of strain relaxation through the entire InxGa1−xN SB-templates. The SB approach results in superior material quality relative to the bulk grown InGaN, mainly due to its ability to avoid the inclusion of indium-rich clusters and V-pits in the SB templates. The SB approach slows down the relaxation processes and templates as thick as 750 nm are not fully relaxed. We are reporting on methods to enhance the relaxation processes in InxGa1−xN SB-templates. Finally, when InxGa1−xN templates with 0 ≤ x ≤ 0.16 are used as substrates for InGaN/GaN multiple quantum wells, the emission wavelength is shifted from blue to green by changing the indium content in the InxGa1−xN SB-templates. To the best of our knowledge, the current results present the highest indium content reported in InxGa1−xN SB-templates.}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Abdelhamid, Mostafa and Reynolds, J. G. and El-Masry, N. A. and Bedair, S. M.}, year={2019}, month={Aug}, pages={18–26} }
 @article{khafagy_hatem_bedair_2019, title={Modelling of III-Nitride Epitaxial Layers Grown on Silicon Substrates with Low Dislocation-Densities}, volume={4}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2019.49}, number={13}, journal={MRS ADVANCES}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2019}, pages={755–760} }
 @article{sayed_bedair_2019, title={Quantum Well Solar Cells: Principles, Recent Progress, and Potential}, volume={9}, ISSN={["2156-3381"]}, DOI={10.1109/JPHOTOV.2019.2892079}, abstractNote={Quantum well solar cells, as a promising approach for next-generation photovoltaic technology, have received great attention in the last few years. Recent developments in materials growth and device structures of quantum wells have opened up new avenues for the incorporation of quantum well structures in next-generation III/V multi-junction solar cells. In this paper, the advantages and challenges of growing quantum wells in the unintentionally doped (i) region of p-i-n solar cells are reviewed. We focus on the recent progress in 1.1–1.3 eV strain-balanced InGaAs/GaAsP, 1.6–1.8 eV strain-balanced and lattice-matched InGaAsP/InGaP, and >2.1 eV strained InGaN/GaN quantum well solar cells, including optimization of the quantum well growth conditions and improving the solar cell structure. For each material system, the challenges associated with materials growth and device performance such as critical layer thickness constraints, strain balance, bandgap tunability, and carrier transport limitations, are discussed. The performance of each quantum well solar cell is compared with bulk absorber operating in the same bandgap range, with the advantages of each being highlighted. The effect of the unintentional background doping on carrier collection (by drift) is presented through modeling and recent experimental results. The recent strategies to enhance the electric field distribution across the quantum well region are reviewed. The potential of incorporating quantum well structures in next-generation multi-junction devices is also discussed.}, number={2}, journal={IEEE JOURNAL OF PHOTOVOLTAICS}, author={Sayed, Islam and Bedair, S. M.}, year={2019}, month={Mar}, pages={402–423} }
 @article{khafagy_hatem_bedair_2018, title={Impact of embedded voids on thin-films with high thermal expansion coefficients mismatch}, volume={112}, ISSN={["1077-3118"]}, DOI={10.1063/1.5011394}, abstractNote={Using technology to reduce defects at heterogeneous interfaces of thin-films is at a high-priority for modern semiconductors. The current work utilizes a three-dimensional multiple-slip crystal-plasticity model and specialized finite-element formulations to study the impact of the embedded void approach (EVA) to reduce defects in thin-films deposited on a substrate with a highly mismatched thermal expansion coefficient, in particular, the growth of an InGaN thin-film on a Si substrate, where EVA has shown a remarkable reduction in stresses on the side of the embedded voids.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2018}, month={Jan} }
 @article{khafagy_hatem_bedair_2018, title={Three-Dimensional Crystal-Plasticity Based Model for Intrinsic Stresses in Multi-junction Photovoltaic}, ISBN={["978-3-319-72361-7"]}, ISSN={["2367-1181"]}, DOI={10.1007/978-3-319-72362-4_41}, abstractNote={Our understanding for intrinsic stresses and defects evolution in photovoltaic devices has became an essential part of new developments. In particular, Multi-Junction Photovoltaic (MJ-PV) modules depend on multi-layer structures that may suffer high dislocation-densities as a result of high lattice and thermal expansion coefficient mismatch. These defects limit the performance, reliability, and lifetime of PV devices. In the current study, a three-dimensional multiple-slip crystal-plasticity model and specialized finite-element formulations are used to investigate InGaN growth on Si substrates. The formulation is based on accounting for thermal and intrinsic stresses as a result of different processing conditions and microstructures. Furthermore, the formulation was used to investigate a recently developed technique, Embedded Void Approach (EVA), which can be used to address both the high density of defects and the cracking/bowing of InGaN growth on Si. The current work lays the groundwork for more extensive use of silicon in MJ-PV devices.}, journal={ENERGY TECHNOLOGY 2018: CARBON DIOXIDE MANAGEMENT AND OTHER TECHNOLOGIES}, author={Khafagy, Khaled H. and Hatem, Tarek M. and Bedair, Salah M.}, year={2018}, pages={453–461} }
 @misc{colter_hagar_bedair_2018, title={Tunnel Junctions for III-V Multijunction Solar Cells Review}, volume={8}, ISSN={["2073-4352"]}, DOI={10.3390/cryst8120445}, abstractNote={Tunnel Junctions, as addressed in this review, are conductive, optically transparent semiconductor layers used to join different semiconductor materials in order to increase overall device efficiency. The first monolithic multi-junction solar cell was grown in 1980 at NCSU and utilized an AlGaAs/AlGaAs tunnel junction. In the last 4 decades both the development and analysis of tunnel junction structures and their application to multi-junction solar cells has resulted in significant performance gains. In this review we will first make note of significant studies of III-V tunnel junction materials and performance, then discuss their incorporation into cells and modeling of their characteristics. A Recent study implicating thermally activated compensation of highly doped semiconductors by native defects rather than dopant diffusion in tunnel junction thermal degradation will be discussed. AlGaAs/InGaP tunnel junctions, showing both high current capability and high transparency (high bandgap), are the current standard for space applications. Of significant note is a variant of this structure containing a quantum well interface showing the best performance to date. This has been studied by several groups and will be discussed at length in order to show a path to future improvements.}, number={12}, journal={CRYSTALS}, author={Colter, Peter and Hagar, Brandon and Bedair, Salah}, year={2018}, month={Dec} }
 @article{sayed_jain_steiner_geisz_bedair_2017, title={100-period InGaAsP/InGaP superlattice solar cell with sub-bandgap quantum efficiency approaching 80%}, volume={111}, ISSN={["1077-3118"]}, DOI={10.1063/1.4993888}, abstractNote={InGaAsP/InGaP quantum well (QW) structures are promising materials for next generation photovoltaic devices because of their tunable bandgap (1.50–1.80 eV) and being aluminum-free. However, the strain-balance limitations have previously limited light absorption in the QW region and constrained the external quantum efficiency (EQE) values beyond the In0.49Ga0.51P band-edge to less than 25%. In this work, we show that implementing a hundred period lattice matched InGaAsP/InGaP superlattice solar cell with more than 65% absorbing InGaAsP well resulted in more than 2× improvement in EQE values than previously reported strain balanced approaches. In addition, processing the devices with a rear optical reflector resulted in strong Fabry-Perot resonance oscillations and the EQE values were highly improved in the vicinity of these peaks, resulting in a short circuit current improvement of 10% relative to devices with a rear optical filter. These enhancements have resulted in an InGaAsP/InGaP superlattice solar cell with improved peak sub-bandgap EQE values exceeding 75% at 700 nm, an improvement in the short circuit current of 26% relative to standard InGaP devices, and an enhanced bandgap-voltage offset (Woc) of 0.4 V.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Sayed, Islam E. H. and Jain, Nikhil and Steiner, Myles A. and Geisz, John F. and Bedair, S. M.}, year={2017}, month={Aug} }
 @article{el-masry_zavada_reynolds_reynolds_liu_bedair_2017, title={Electric field control of ferromagnetism at room temperature in GaCrN (p-i-n) device structures}, volume={111}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4986431}, DOI={10.1063/1.4986431}, abstractNote={We have demonstrated a room temperature dilute magnetic semiconductor based on GaCrN epitaxial layers grown by metalorganic chemical vapor deposition. Saturation magnetization Ms increased when the GaCrN film is incorporated into a (p-GaN/i-GaCrN/n-GaN) device structure, due to the proximity of mediated holes present in the p-GaN layer. Zero field cooling and field cooling were measured to ascertain the absence of superparamagnetic behavior in the films. A (p-GaN/i-GaCrN/n-GaN) device structure with room temperature ferromagnetic (FM) properties that can be controlled by an external applied voltage has been fabricated. In this work, we show that the applied voltage controls the ferromagnetic properties, by biasing the (p-i-n) structure. With forward bias, ferromagnetism in the GaCrN layer was increased nearly 4 fold of the original value. Such an enhancement is due to carrier injection of holes into the Cr deep level present in the i-GaCrN layer. A “memory effect” for the FM behavior of the (p-i-n) GaCrN device structure persisted for 42 h after the voltage bias was turned off. These measurements also support that the observed ferromagnetism in the GaCrN film is not due to superparamagnetic clusters but instead is a hole-mediated phenomenon.}, number={8}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={El-Masry, N. A. and Zavada, J. M. and Reynolds, J. G. and Reynolds, C. L., Jr. and Liu, Z. and Bedair, S. M.}, year={2017}, month={Aug}, pages={082402} }
 @inproceedings{bedair_harmon_carlin_sayed_colter_2016, title={Annealed high band gap tunnel junctions with peak current densities above 800 A/cm(2)}, DOI={10.1109/pvsc.2016.7750052}, abstractNote={The development of high-performance high band gap tunnel junctions is critical for producing efficient multijunction photovoltaic cells that can operate at high solar concentrations. The n-InGaP/GaAs/p-AlGaAs TJ has been demonstrated to produce peak tunneling currents (J pk ) above 1000 A/cm2 with minimal absorption losses due to the use of thin (≤50 A) GaAs layer. We will report on the growth and device modeling of these structures as well as the effect of high temperature annealing on J pk . A method to grow TJ structures resistant to annealing will be described, which has resulted in thermally annealed TJ with J pk above 800 A/cm2. This is the highest value ever reported for an annealed high band gap TJ. Device modeling has been used to investigate the source of the high tunneling current, as well as the behavior of the annealed TJ.}, booktitle={2016 ieee 43rd photovoltaic specialists conference (pvsc)}, author={Bedair, S. M. and Harmon, J. L. and Carlin, C. Z. and Sayed, I. E. H. and Colter, P. C.}, year={2016}, pages={2320–2322} }
 @inproceedings{sayed_hagar_carlin_colter_bedair_2016, title={Extending the absorption threshold of InGaP solar cells to 1.60 eV using quantum wells: experimental and modeling results}, DOI={10.1109/pvsc.2016.7750063}, abstractNote={Strain balanced multiple quantum wells (SBMQWs) lattice matched to GaAs consisting of InGaAsP wells balanced with InGaP barriers have been used to extend the absorption of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.49</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.51</sub> P subcells to longer wavelengths for use in five and six junction photovoltaic devices. Thin layers of InGaAsP quantum wells that absorb beyond 760 nm, have been grown with compositions within the miscibility gap of InGaAsP while maintaining thermodynamic stability. External quantum efficiency and current-voltage measurements reveal that InGaAsP/InGaP SBMQWs extend absorption beyond the InGaP band-edge and improve the short circuit current with minimal degradation of open circuit voltage. We study the effect of barrier height on the carrier transport through altering the Indium percentage in the InGaP barrier. Three samples of different barrier heights are fabricated and compared with each other. Results indicate that with proper design of the layers thicknesses and compositions, the absorption threshold of InGaP can be extended up to 780 nm (~1.59 eV). The promising results of InGaAsP/InGaP SBMQWs in this work offer tremendous potential to alleviate current matching restrictions in next generation and current photovoltaic devices.}, booktitle={2016 ieee 43rd photovoltaic specialists conference (pvsc)}, author={Sayed, I. E. H. and Hagar, B. G. and Carlin, C. Z. and Colter, P. C. and Bedair, S. M.}, year={2016}, pages={2366–2370} }
 @article{bedair_carlin_harmon_sayed_colter_2016, title={High Performance Tunnel Junction with Resistance to Thermal Annealing}, volume={1766}, ISSN={["0094-243X"]}, DOI={10.1063/1.4962071}, abstractNote={The availability of high band gap (>1.9 eV) tunnel junctions (TJ) with large peak current densities (Jpk) is crucial for the development of multijunction photovoltaic cells that can operate at concentrations above 1000 suns. Existing TJ designs include thick GaAs layers which reduce the overall efficiency due to absorption. We have developed an n-InGaP/GaAs/p-AlGaAs structure with a GaAs layer that is 50 Å or thinner that has an as-grown Jpk above 2000 A/cm2 an annealed Jpk above 1000 A/cm2. Due to the memory effect of the Te n-type dopant, modifications to the shut off time of the DETe precursor produced the high Jpk that was observed.}, journal={12TH INTERNATIONAL CONFERENCE ON CONCENTRATOR PHOTOVOLTAIC SYSTEMS (CPV-12)}, author={Bedair, S. M. and Carlin, C. Zachary and Harmon, Jeffrey L. and Sayed, Islam E. Hashem and Colter, P. C.}, year={2016} }
 @article{bedair_harmon_carlin_sayed_colter_2016, title={High performance as-grown and annealed high band gap tunnel junctions: Te behavior at the interface}, volume={108}, ISSN={["1077-3118"]}, DOI={10.1063/1.4951690}, abstractNote={The performance of n+-InGaP(Te)/p+-AlGaAs(C) high band gap tunnel junctions (TJ) is critical for achieving high efficiency in multijunction photovoltaics. Several limitations for as grown and annealed TJ can be attributed to the Te doping of InGaP and its behavior at the junction interface. Te atoms in InGaP tend to get attached at step edges, resulting in a Te memory effect. In this work, we use the peak tunneling current (Jpk) in this TJ as a diagnostic tool to study the behavior of the Te dopant at the TJ interface. Additionally, we used our understanding of Te behavior at the interface, guided by device modeling, to modify the Te source shut-off procedure and the growth rate. These modifications lead to a record performance for both the as-grown (2000 A/cm2) and annealed (1000 A/cm2) high band gap tunnel junction.}, number={20}, journal={APPLIED PHYSICS LETTERS}, author={Bedair, S. M. and Harmon, Jeffrey L. and Carlin, C. Zachary and Sayed, Islam E. Hashem and Colter, P. C.}, year={2016}, month={May} }
 @inproceedings{sayed_hagar_carlin_colter_bedair_2016, title={InGaP-based quantum well solar cells}, DOI={10.1109/pvsc.2016.7749566}, abstractNote={Quantum well structures hold tremendous potential in taking next step beyond current photovoltaic structures in achieving solar conversion efficiencies beyond 50%. In this paper we investigate p-i-n InGaP solar cells incorporating InGaAsP/InGaP strain balanced multiple quantum wells (SBMQWs) to tune the absorption threshold beyond the In0.49Ga0.51P cut-off (~ 1.85 eV). The effects of quantum well number and thickness on the optoelectronic properties of InGaAsP/InGaP SBMQWs are investigated. Specifically, we investigate the bandgap tunability of these SBMQW devices by varying well and barrier thickness. Spectral response measurements reveal that longer excitonic absorption with efficient carrier transport can be realized if proper materials compositions and thicknesses are realized. In addition, InGaP p-i-n solar cells including various numbers of InGaAsP/InGaP SBMQWs with an effective bandgap of 1.65 eV in the intrinsic (i) layer were fabricated and characterized. With up to 30 quantum wells, spectral response and light I-V measurements reveal an improvement in the excitonic absorption and short circuit current in comparison to the standard device. The promising results in this work provide an alternative path for realizing 1.5-1.8 eV subcells in next-generation multi-junction solar cells.}, booktitle={2016 ieee 43rd photovoltaic specialists conference (pvsc)}, author={Sayed, I. E. H. and Hagar, B. G. and Carlin, C. Z. and Colter, P. C. and Bedair, S. M.}, year={2016}, pages={147–150} }
 @article{hashem_carlin_hagar_colter_bedair_2016, title={InGaP-based quantum well solar cells: Growth, structural design, and photovoltaic properties}, volume={119}, ISSN={["1089-7550"]}, DOI={10.1063/1.4943366}, abstractNote={Raising the efficiency ceiling of multi-junction solar cells (MJSCs) through the use of more optimal band gap configurations of next-generation MJSC is crucial for concentrator and space systems. Towards this goal, we propose two strain balanced multiple quantum well (SBMQW) structures to tune the bandgap of InGaP-based solar cells. These structures are based on InxGa1−xAs1−zPz/InyGa1−yP (x > y) and InxGa1−xP/InyGa1−yP (x > y) well/barrier combinations, lattice matched to GaAs in a p-i-n solar cell device. The bandgap of InxGa1−xAs1−zPz/InyGa1−yP can be tuned from 1.82 to 1.65 eV by adjusting the well composition and thickness, which promotes its use as an efficient subcell for next generation five and six junction photovoltaic devices. The thicknesses of wells and barriers are adjusted using a zero net stress balance model to prevent the formation of defects. Thin layers of InGaAsP wells have been grown thermodynamically stable with compositions within the miscibility gap for the bulk alloy. The growth conditions of the two SBMQWs and the individual layers are reported. The structures are characterized and analyzed by optical microscopy, X-ray diffraction, photoluminescence, current-voltage characteristics, and spectral response (external quantum efficiency). The effect of the well number on the excitonic absorption of InGaAsP/InGaP SBMQWs is discussed and analyzed.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hashem, Islam E. and Carlin, C. Zachary and Hagar, Brandon G. and Colter, Peter C. and Bedair, S. M.}, year={2016}, month={Mar} }
 @article{sayed_carlin_hagar_colter_bedair_2016, title={Strain-Balanced InGaAsP/GaInP Multiple Quantum Well Solar Cells With a Tunable Bandgap (1.65-1.82 eV)}, volume={6}, ISSN={["2156-3381"]}, DOI={10.1109/jphotov.2016.2549745}, abstractNote={Currently available materials for III–V multijunction solar cells lattice matched to GaAs covering the spectral range from 1.65 to 1.82 eV are composed of either immiscible quaternary alloys or contain aluminum. We report the fabrication of a novel aluminum-free In <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_x$</tex-math></inline-formula> Ga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{1-x}$</tex-math></inline-formula> As <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{1-z}$</tex-math></inline-formula> P <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_z$ </tex-math></inline-formula> /Ga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{1-y}$</tex-math></inline-formula> In <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_y$</tex-math></inline-formula> P ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> > <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> ) strain-balanced multiple quantum-well (SBMQW) p-i-n solar cell structure lattice matched to GaAs, grown by metal–organic chemical vapor deposition. SBMQWs consist of alternating layers of In <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_x$</tex-math></inline-formula> Ga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{1-x}$ </tex-math></inline-formula> As <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{1-z}$</tex-math></inline-formula> P <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_z$</tex-math></inline-formula> wells and Ga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{1-y}$</tex-math></inline-formula> In <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_y$ </tex-math></inline-formula> P barriers ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> > <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> ) under compressive and tensile strain, respectively. When compared with standard GaInP devices, SBMQW structures exhibit longer photoluminescence wavelength (680–780 nm) emission and enhanced light absorption with improved short-circuit current density. In this study, the SBMQW emission and absorption wavelength is controlled by adjusting the layer thickness of InGaAsP wells, while the arsenic and indium compositions are fixed. We show that carriers generated in QWs are extracted via thermionic emission. The proposed SBMQWs allow more flexibility in the design of current multijunction solar cells and future cells with more than four junctions. InGaAsP/GaInP SBMQWs may also be used in applications other than solar cells, such as light-emitting diodes (LEDs) and lasers, with the advantages of tuning the emission and absorption processes.}, number={4}, journal={IEEE JOURNAL OF PHOTOVOLTAICS}, author={Sayed, Islam E. Hashem and Carlin, Conrad Zachary and Hagar, Brandon G. and Colter, Peter C. and Bedair, S. M.}, year={2016}, month={Jul}, pages={997–1003} }
 @article{van den broeck_bharrat_liu_el-masry_bedair_2015, title={Growth and Characterization of High-Quality, Relaxed In (y) Ga1-y N Templates for Optoelectronic Applications}, volume={44}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-015-3989-9}, number={11}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Van Den Broeck, D. M. and Bharrat, D. and Liu, Z. and El-Masry, N. A. and Bedair, S. M.}, year={2015}, month={Nov}, pages={4161–4166} }
 @inproceedings{sayed_carlin_hagar_colter_bedair_2015, title={Tunable GaInP solar cell lattice matched to GaAs}, DOI={10.1109/pvsc.2015.7356081}, abstractNote={A new strain-balanced multiple quantum well (MQW) approach to tune the Ga0.51In0.49P bandgap is demonstrated. This approach is based on Ga1−xInxP/Ga1−yInyP (x > y) or Ga1−xInxAszP1−z/Ga1−yInyP (x > y) structures, strain balanced and lattice matched to GaAs in a p-i-n solar cell structure. A red shift in the absorption edge and an increase in the short circuit current were observed. Carriers generated in quantum wells due to transitions between the quantum levels are transported across the barriers via thermionic emission. The proposed structure allows more flexibility in the design of current multi-junction solar cells and future cells with more than four junctions.}, booktitle={2015 ieee 42nd photovoltaic specialist conference (pvsc)}, author={Sayed, I. E. H. and Carlin, C. Z. and Hagar, B. and Colter, P. C. and Bedair, S. M.}, year={2015} }
 @article{bradshaw_samberg_carlin_colter_edmondson_hong_fetzer_karam_bedair_2014, title={GaInP/GaAs Tandem Solar Cells With InGaAs/GaAsP Multiple Quantum Wells}, volume={4}, ISSN={["2156-3403"]}, DOI={10.1109/jphotov.2013.2294750}, abstractNote={Lattice-matched multiple quantum wells (MQWs) consisting of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As wells with very thin GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> barriers have been incorporated into a GaInP/GaAs tandem solar cell. InGaAs/GaAsP MQWs increase the short-circuit current of the GaAs cell by extending the absorption range, with minimal impact on an open-circuit voltage, thus alleviating current matching restrictions placed by the GaAs cell on multijunction solar cells. MQWs with very thin, tensile strained, high phosphorus content GaAsP barriers allow tunneling to dominate carrier transport across the MQWs and balance the compressive strain of the InGaAs wells such that material quality remains high for subsequent top cell growth. We show that the addition of the QW layers enhances the GaAs cell, does not degrade the performance of the GaInP top cell, and leads to potential efficiency enhancements.}, number={2}, journal={IEEE JOURNAL OF PHOTOVOLTAICS}, author={Bradshaw, Geoffrey K. and Samberg, Joshua P. and Carlin, C. Zachary and Colter, Peter C. and Edmondson, Kenneth M. and Hong, William and Fetzer, Chris and Karam, Nasser and Bedair, Salah M.}, year={2014}, month={Mar}, pages={614–619} }
 @inbook{bain_hosalli_bedair_paskova_ivanisevic_2014, place={Cham, Switzerland}, series={Conference Proceedings of the Society for Experimental Mechanics Series}, title={Molecular Interactions on InxGa1−xN}, volume={5}, ISBN={9783319007793 9783319007809}, ISSN={2191-5644 2191-5652}, url={http://dx.doi.org/10.1007/978-3-319-00780-9_14}, DOI={10.1007/978-3-319-00780-9_14}, abstractNote={Atomic force microscopy in solution offers a platform for assessing interactions on chemically modified surfaces. In this study a biologically relevant molecule, an amino acid, is adsorbed onto a compositionally varied semiconductor substrate. AFM is used to assess the effect of the substrate composition on the adhesion of the amino acid. We report adsorption of L-arginine to an indium-gallium-nitride (InGaN) substrate with a gradient of In:Ga composition. Data are collected above and below the isoelectric point of arginine to highlight the effect of protonation on the adhesive behavior across the InGaN. Characterization is also performed using X-ray photoelectron spectroscopy to establish the presence of amino acid on the surface and determine the general composition of a given region of the substrate both with and without amino acid. Combining these factors, we are able to better evaluate the significance of substrate properties in influencing the behavior of surface molecules. Determining the dynamics of amino acid behavior as a function of both the substrate and the environment provides new insight into the preparation of semiconductor materials for biological applications.}, booktitle={MEMS and Nanotechnology}, publisher={Springer International Publishing}, author={Bain, L. E. and Hosalli, A. M. and Bedair, S. M. and Paskova, T. and Ivanisevic, A.}, editor={Shaw, G., III and Prorok, B. and Starman, L. and Furlong, C.Editors}, year={2014}, pages={109–114}, collection={Conference Proceedings of the Society for Experimental Mechanics Series} }
 @article{broeck_bharrat_hosalli_el-masry_bedair_2014, title={Strain-balanced InGaN/GaN multiple quantum wells}, volume={105}, ISSN={["1077-3118"]}, DOI={10.1063/1.4890738}, abstractNote={InGaN/GaN multiple quantum well (MQW) structures suffer from a high amount of compressive strain in the InGaN wells and the accompanied piezoelectric field resulting in both a blue shift in emission and a reduction of emission intensity. We report the growth of InxGa1−xN/GaN “strain-balanced” multiple quantum wells (SBMQWs) grown on thick InyGa1−yN templates for x > y by metal organic chemical vapor deposition. SBMQWs consist of alternating layers of InxGa1−xN wells and GaN barriers under compressive and tensile stress, respectively, which have been lattice matched to a thick InyGa1−yN template. Growth of the InyGa1−yN template is also detailed in order to achieve thick, relaxed InyGa1−yN grown on GaN without the presence of V-grooves. When compared to conventional InxGa1−xN/GaN MQWs grown on GaN, the SBMQW structures exhibit longer wavelength emission and higher emission intensity for the same InN mole fraction due to a reduction in the well strain and piezoelectric field. By matching the average lattice constant of the MQW active region to the lattice constant of the InyGa1−yN template, essentially an infinite number of periods can be grown using the SBMQW growth method without relaxation-related effects. SBMQWs can be utilized to achieve longer wavelength emission in light emitting diodes without the use of excess indium and can be advantageous in addressing the “green gap.”}, number={3}, journal={APPLIED PHYSICS LETTERS}, author={Broeck, D. M. and Bharrat, D. and Hosalli, A. M. and El-Masry, N. A. and Bedair, S. M.}, year={2014}, month={Jul} }
 @article{bain_jewett_mukund_bedair_paskova_ivanisevic_2013, title={Biomolecular Gradients via Semiconductor Gradients: Characterization of Amino Acid Adsorption to InxGa1–xN Surfaces}, volume={5}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/AM4015555}, DOI={10.1021/AM4015555}, abstractNote={The band gap of indium gallium nitride can be tuned by varying the compositional ratio of indium to gallium, spanning the entire visible region and extending into the near-infrared and near-ultraviolet. This tunability allows for device optimization specific to different applications, including as a biosensor or platform for studying biological interactions. However, these rely on chemically dependent interactions between the device surface and the biostructures of interest. This study presents a material gradient of changing In:Ga composition and the subsequent evaluation of amino acid adsorption to this surface. Arginine is adsorbed to the surface in conditions both above and below the isoelectric point, providing insight to the role of electrostatic interactions in interface formation. These electrostatics are the driving force of the observed adsorption behaviors, with protonated amino acid demonstrating increased adsorption as a function of native surface oxide buildup. We thus present a gradient inorganic substrate featuring varying affinity for amino acid adhesion, which can be applied in generating gradient architectures for biosensors and studying cellular behaviors without application of specialized patterning processes.}, number={15}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Bain, Lauren E and Jewett, Scott A and Mukund, Aadhithya Hosalli and Bedair, Salah M and Paskova, Tania M and Ivanisevic, Albena}, year={2013}, month={Jul}, pages={7236–7243} }
 @article{bradshaw_carlin_samberg_el-masry_colter_bedair_2013, title={Carrier Transport and Improved Collection in Thin-Barrier InGaAs/GaAsP Strained Quantum Well Solar Cells}, volume={3}, ISSN={["2156-3381"]}, DOI={10.1109/jphotov.2012.2216858}, abstractNote={Multiple quantum wells (MQW) lattice matched to GaAs consisting of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.14</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.76</sub> As wells balanced with GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.24</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.76</sub> barriers have been used to extend the absorption of GaAs subcells to longer wavelengths for use in an InGaP/GaAs/Ge triple-junction photovoltaic cell. Thin barriers with high-phosphorus composition are capable of balancing the strain from the InGaAs wells; thus, creating conditions to allow for thicker wells and for carrier tunneling to dominate transport across the structure. As a result, a larger percentage of the depletion region is occupied by InGaAs quantum wells that absorb wavelengths beyond 875 nm and the indium composition is not limited by thermionic emission requirements. Measurements at elevated temperatures and reverse bias suggest that a thermally assisted tunneling mechanism is responsible for transport through the barriers.}, number={1}, journal={IEEE JOURNAL OF PHOTOVOLTAICS}, author={Bradshaw, Geoffrey K. and Carlin, C. Zachary and Samberg, Joshua P. and El-Masry, Nadia A. and Colter, Peter C. and Bedair, Salah M.}, year={2013}, month={Jan}, pages={278–283} }
 @inproceedings{bradshaw_carlin_samberg_colter_bedair_2013, title={Determination of carrier recombination lifetime in InGaAs quantum wells from external quantum efficiency measurements}, DOI={10.1109/pvsc.2013.6744143}, abstractNote={GaAs cells containing multiple quantum wells (MQW) of strained InGaAs/GaAsP can enhance efficiency in multijunction solar cells. Determination of carrier recombination lifetime in the InGaAs well is useful to understand material quality and carrier transport across the structure. GaAs p-i-n structures with and without strain balanced In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.17</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.83</sub> As wells and GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.25</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> barriers were grown by MOCVD on p-type GaAs substrates. The GaAsP barrier thickness was varied between devices to intentionally influence carrier transport. A decrease in EQE was observed as barrier width was increased, which was attributed to an increase in tunneling lifetime, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tn</sub> . While this EQE decrease is undesirable in practical devices, it is useful for determining the recombination lifetime, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , of the InGaAs wells. The decrease in EQE was observed only at wavelengths of light greater than 600 nm, indicating that minority carrier electrons generated in the base are responsible for the reduction in EQE. Shorter wavelengths (<;600 nm) of light are almost completely absorbed before reaching the base and primarily generate holes in the emitter. The tunneling lifetime and the currents generated in the p-i-n structures were modeled to calculate the EQE of a GaAs control and both thick and thin barrier MQW devices. The probability of transport through the entire MQW structure, P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tot</sub> , was varied until the calculated EQE fit the experimental data. The value of P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tot</sub> was then correlated to the only unknown parameter, the recombination lifetime. Using this method the recombination lifetime in In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.17</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.83</sub> As in the QW was determined to be 110 ns, which agrees with values found in previous time resolved photoluminescence measurements of metamorphic InGaAs films.}, booktitle={2013 ieee 39th photovoltaic specialists conference (pvsc)}, author={Bradshaw, G. K. and Carlin, C. Z. and Samberg, J. P. and Colter, P. C. and Bedair, S. M.}, year={2013}, pages={264–267} }
 @article{samberg_carlin_bradshaw_colter_harmon_allen_hauser_bedair_2013, title={Effect of GaAs interfacial layer on the performance of high bandgap tunnel junctions for multijunction solar cells}, volume={103}, ISSN={["1077-3118"]}, DOI={10.1063/1.4819917}, abstractNote={The effect of the heterojunction interface on the performance of high bandgap InxGa1−xP:Te/Al0.6Ga0.4As:C tunnel junctions (TJs) was investigated. The insertion of 30 Å of GaAs:Te at the junction interface resulted in a peak current of 1000 A/cm2 and a voltage drop of ∼3 mV for 30 A/cm2 (2000× concentration). The presence of this GaAs interfacial layer also improved the uniformity across the wafer. Modeling results are consistent with experimental data and were used to explain the observed enhancement in TJ performance. This architecture could be used within multijunction solar cells to extend the range of usable solar concentration with minimal voltage drop.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Samberg, Joshua P. and Carlin, C. Zachary and Bradshaw, Geoff K. and Colter, Peter C. and Harmon, Jeffrey L. and Allen, J. B. and Hauser, John R. and Bedair, S. M.}, year={2013}, month={Sep} }
 @article{bharrat_hosalli_van den broeck_samberg_bedair_el-masry_2013, title={Gallium nitride nanowires by maskless hot phosphoric wet etching}, volume={103}, ISSN={["1077-3118"]}, DOI={10.1063/1.4819272}, abstractNote={We demonstrate gallium nitride (GaN) nanowires formation by controlling the selective and anisotropic etching of N-polar GaN in hot phosphoric acid. Nanowires of ∼109/cm,2 total height of ∼400 nm, and diameters of 170–200 nm were obtained. These nanowires have both non-polar {11¯00}/ {112¯0} and semi-polar {1011¯} facets. X–Ray Diffraction characterization shows that screw dislocations are primarily responsible for preferential etching to create nanowires. Indium gallium nitride multi-quantum wells (MQWs) grown on these GaN nanowires showed a blue shift in peak emission wavelength of photoluminescence spectra, and full width at half maximum decreased relative to MQWs grown on planar N-polar GaN, respectively.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Bharrat, D. and Hosalli, A. M. and Van Den Broeck, D. M. and Samberg, J. P. and Bedair, S. M. and El-Masry, N. A.}, year={2013}, month={Aug} }
 @article{samberg_carlin_bradshaw_colter_bedair_2013, title={Growth and Characterization of InxGa1-xAs/GaAs1-yPy Strained-Layer Superlattices with High Values of y (similar to 80%)}, volume={42}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-012-2375-0}, abstractNote={Strained-layer superlattice (SLS) structures, such as InGaAs/GaAsP lattice matched to GaAs, have shown great potential in absorption devices such as photodetectors and triple-junction photovoltaic cells. However, until recently they have been somewhat hindered by their usage of low-phosphorus GaAsP barriers. High-P-composition GaAsP was developed as the barrier for InGaAs/GaAsP strained-layer superlattice (SLS) structures, and the merits of using such a high composition of phosphorus are discussed. It is believed that these barriers represent the highest phosphorus content to date in such a structure. By using high-composition GaAsP the carriers are collected via tunneling (for barriers ≤30 Å) as opposed to thermionic emission. Thus, by utilizing thin, high-content GaAsP barriers one can increase the percentage of the intrinsic in a p-i-n structure that is composed of InGaAs wells in addition to increasing the number of periods that can be grown for given depletion width. However, standard SLSs of this type inherently possess undesirable compressive strain and quantum size effects (QSEs) that cause the optical absorption of the thin InGaAs SLS wells to shift to higher energies relative to that of bulk InGaAs of the same composition. To circumvent these deleterious QSEs, stress-balanced, pseudomorphic InGaAs/GaAsP staggered SLSs were grown. Staggering was achieved by removing a portion of one well and adding it to an adjacent well. The spectral response obtained from device characterization indicated that staggering resulted in thicker InGaAs films with reduced cutoff energy. Additionally, these data confirm that tunneling is a very effective means for carrier transport in the SLS.}, number={5}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Samberg, J. P. and Carlin, C. Z. and Bradshaw, G. K. and Colter, P. C. and Bedair, S. M.}, year={2013}, month={May}, pages={912–917} }
 @article{samberg_alipour_bradshaw_carlin_colter_lebeau_el-masry_bedair_2013, title={Interface properties of Ga(As,P)/(In,Ga)As strained multiple quantum well structures}, volume={103}, ISSN={["0003-6951"]}, DOI={10.1063/1.4818548}, abstractNote={(In,Ga)As/Ga(As,P) multiple quantum wells (MQWs) with GaAs interface layers have been characterized with photoluminescence (PL) and high resolution scanning transmission electron microscopy (STEM). By growing (In,Ga)As/Ga(As,P) MQWs with asymmetric GaAs interfacial layers, we found that phosphorus carry-over had a profound effect on the absorption edge of the (In,Ga)As wells. Evidence for this phosphorus was initially determined via PL and then definitively proven through STEM and energy dispersive x-ray spectroscopy. We show that the phosphorus carry-over can be prevented with sufficiently thick GaAs transition layers. Preliminary results for GaAs p-i-n solar cells utilizing the improved MQWs are presented.}, number={7}, journal={APPLIED PHYSICS LETTERS}, author={Samberg, Joshua P. and Alipour, Hamideh M. and Bradshaw, Geoffrey K. and Carlin, C. Zachary and Colter, Peter C. and LeBeau, James M. and El-Masry, N. A. and Bedair, Salah M.}, year={2013}, month={Aug} }
 @article{hosalli_van den broeck_bharrat_el-masry_bedair_2013, title={Inversion by metalorganic chemical vapor deposition from N- to Ga-polar gallium nitride and its application to multiple quantum well light-emitting diodes}, volume={103}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4841755}, DOI={10.1063/1.4841755}, abstractNote={We demonstrate a metalorganic chemical vapor deposition growth approach for inverting N-polar to Ga-polar GaN by using a thin inversion layer grown with high Mg flux. The introduction of this inversion layer allowed us to grow p-GaN films on N-polar GaN thin film. We have studied the dependence of hole concentration, surface morphology, and degree of polarity inversion for the inverted Ga-polar surface on the thickness of the inversion layer. We then use this approach to grow a light emitting diode structure which has the MQW active region grown on the advantageous N-polar surface and the p-layer grown on the inverted Ga-polar surface.}, number={23}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Hosalli, A. M. and Van Den Broeck, D. M. and Bharrat, D. and El-Masry, N. A. and Bedair, S. M.}, year={2013}, month={Dec}, pages={231108} }
 @article{carlin_bradshaw_samberg_colter_bedair_2013, title={Minority Carrier Transport and Their Lifetime in InGaAs/GaAsP Multiple Quantum Well Structures}, volume={60}, ISSN={["1557-9646"]}, DOI={10.1109/ted.2013.2268421}, abstractNote={Minority carrier transport across InGaAs/GaAsP multiple quantum wells is studied by measuring the response of p-i-n and n-i-p GaAs solar cell structures. It is observed that the spectral response depends critically upon the width of the GaAsP barriers and the device polarity. Electron tunneling is not as efficient as hole tunneling due to a higher conduction band barrier. The spectral response depends on the relative magnitude of the carrier lifetime as compared with the tunneling lifetime. This paper deduces an estimated electron lifetime of 110 ns in In0.14Ga0.86As wells and 25 ns in In0.17Ga0.83As wells, which agree with published results.}, number={8}, journal={IEEE TRANSACTIONS ON ELECTRON DEVICES}, author={Carlin, Conrad Zachary and Bradshaw, Geoffrey Keith and Samberg, Joshua Paul and Colter, Peter C. and Bedair, Salah M.}, year={2013}, month={Aug}, pages={2532–2536} }
 @inproceedings{hauser_carlin_harmon_bradshaw_samberg_colter_bedair_2013, title={Modeling an InGaP/AlGaAs tunnel junction containing an AlAs diffusion barrier}, DOI={10.1109/pvsc.2013.6744883}, abstractNote={Cost improvements in concentrated photovoltaic (CPV) systems can be achieved by operating at increased solar concentration. Current multijunction CPV systems are limited to about 1000× concentration by the performance of the tunnel junctions (TJ) which connect the subcells. The TJ requires materials which are doped in excess of 1019 cm-3 in order to operate effectively, and so are susceptible to diffusion during the growth of subsequent layers. This paper considers a tunnel junction comprised of tellurium doped n+-InGaP and carbon doped p+-AlGaAs with a several monolayers of AlAs at the interface. The diffusion profile of the dopants was found and used to calculate the tunneling current through a junction. Due to uncertainty in the diffusion constants of C and Te in the three layers, the tunneling current was calculated for several values of Dt. The diffusion constant ratio in the AlAs was taken as a fraction of the diffusion constant in the other two layers. A significant increase in peak tunneling current was seen for Dt>1×10-14 cm2 when a three monolayer thick AlAs barrier was present.}, booktitle={2013 ieee 39th photovoltaic specialists conference (pvsc)}, author={Hauser, J. and Carlin, Z. and Harmon, J. and Bradshaw, G. and Samberg, J. and Colter, P. and Bedair, S.}, year={2013}, pages={2082–2085} }
 @article{frajtag_nepal_paskova_bedair_el-masry_2013, title={Multifacet semipolar formation by controlling the groove depth via lateral sidewall epitaxy}, volume={367}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2012.12.039}, abstractNote={We demonstrate InxGa1−xN/GaN light emitting diode structures with different sets of multifacet semipolar formation grown laterally on m-plane sidewalls formed by stripe patterning on preliminary grown c-plane GaN template. It was found that regrowth on shallow side walls within the GaN template resulted in a single semipolar (11¯01) facet, while deeper side walls led to multifacet semipolar formation. Very deep etching through the entire GaN template reaching the underlying sapphire substrates resulted in a combination of semipolar (11¯01) and nonpolar (11¯00) facets. The results indicate that the depth of the groove patterning can be used as a tool for controlling the set of semipolar facet formation. In addition, the growth rate in different crystallographic directions was studied and possible factors affecting the growth rates are discussed.}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Frajtag, P. and Nepal, N. and Paskova, T. and Bedair, S. M. and El-Masry, N. A.}, year={2013}, month={Mar}, pages={88–93} }
 @article{roberts_mohanta_everitt_leach_broeck_hosalli_paskova_bedair_2013, title={Spectroscopic investigation of coupling among asymmetric InGaN/GaN multiple quantum wells grown on non-polar a-plane GaN substrates}, volume={103}, ISSN={["1077-3118"]}, DOI={10.1063/1.4827536}, abstractNote={Low defect density asymmetric multiple quantum wells (MQWs) of InGaN/GaN grown on non-polar a-plane GaN substrates were investigated using time-integrated and time-resolved photoluminescence spectroscopy. Comparison of these spectra with the predicted emission energies reveals that these QWs may be spectrally resolved at low temperatures. However, a combination of thermal activation and resonant tunneling of carriers increasingly coupled the QWs, favoring emission from the lowest energy QWs with increasing temperature in a manner analogous to MQWs composed of other non-polar semiconductor materials but unlike most InGaN MQWs grown on polar substrates and influenced by the strong polarization-dependent effects.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Roberts, A. T. and Mohanta, A. and Everitt, H. O. and Leach, J. H. and Broeck, D. and Hosalli, A. M. and Paskova, T. and Bedair, S. M.}, year={2013}, month={Oct} }
 @inproceedings{samberg_bradshaw_carlin_colter_edmondson_hong_fetzer_karam_el-masry_bedair_2013, title={Tandem InGaP/GaAs-quantum well solar cells and their potential improvement through phosphorus carry-over management in multiple quantum well structures}, DOI={10.1109/pvsc.2013.6744479}, abstractNote={InGaP/GaAs/Ge multijunction solar cell (MJSC) efficiency can be increased through improved current matching among the subcells with multiple quantum wells (MQWs) being promising for this purpose. In this study we show that InGaAs/GaAsP QWs utilizing high phosphorus composition barriers can be successfully incorporated into the GaAs subcell of an InGaP/GaAs tandem solar cell. This InGaP/GaAs-MQW device has an enhanced short circuit current density when compared to that of a standard InGaP/GaAs tandem device with minimal impact on either GaAs or InGaP subcell open circuit voltage. Additionally, phosphorus carry-over in the MQW structure is investigated through the use of photoluminescence (PL). It is demonstrated that the phosphorus carry-over can be overcome through the utilization of thick GaAs transition layers at the GaAsP→InGaAs interfaces, resulting in a MQW with an extended absorption edge.}, booktitle={2013 ieee 39th photovoltaic specialists conference (pvsc)}, author={Samberg, J. P. and Bradshaw, G. K. and Carlin, C. Z. and Colter, P. C. and Edmondson, K. and Hong, W. and Fetzer, C. and Karam, N. and El-Masry, N. A. and Bedair, S. M.}, year={2013}, pages={1737–1740} }
 @article{frajtag_hosalli_samberg_colter_paskova_el-masry_bedair_2012, title={Overgrowth of GaN on GaN nanowires produced by mask-less etching}, volume={352}, ISSN={["0022-0248"]}, DOI={10.1016/j.jcrysgro.2011.12.055}, abstractNote={We report on the generation of GaN nanowires (NWs) using mask-less reactive ion etching (RIE). The NWs are believed to be the result of a high etching rate in regions where a high dislocation density is present in the GaN films grown on sapphire substrates. We have studied the effect of defect densities in the original GaN films and its relation to the generation of these NWs. We show that defect reduction in the overgrown GaN is related to the presence of a network of embedded voids generated between these nanowires during the regrowth on the etched nanowires. We show that further reduction in dislocation density can be achieved by repeating the process of nanowire generation and overgrowth. Also we report on the residual strain and curvature in GaN after the first and second embedded voids approach (EVA).}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Frajtag, P. and Hosalli, A. M. and Samberg, J. P. and Colter, P. C. and Paskova, T. and El-Masry, N. A. and Bedair, S. M.}, year={2012}, month={Aug}, pages={203–208} }
 @article{liliental-weber_yu_zakharov_bedair_2012, title={Planar defects in thin films of InGaN}, volume={18}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S1431927612009282}, DOI={10.1017/S1431927612009282}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.}, number={S2}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Liliental-Weber, Z. and Yu, K.M. and Zakharov, D. and Bedair, S.}, year={2012}, month={Jul}, pages={1486–1487} }
 @article{frajtag_el-masry_nepal_bedair_2011, title={Embedded voids approach for low defect density in epitaxial GaN films}, volume={98}, ISSN={["1077-3118"]}, DOI={10.1063/1.3540680}, abstractNote={We have developed a technique for defect reduction in GaN epitaxial films grown on sapphire substrates. This technique relies on the generation of high densities of embedded microvoids (∼108/cm2), a few microns long and less than a micron in diameter. These voids are located near the sapphire substrate, where high densities of dislocations are present. Network of embedded voids offer free surfaces that act as dislocation sinks or termination sites for the dislocations generated at the GaN/sapphire interface. Both transmission electron and atomic force microscopy results confirm the uniform reduction of the dislocation density by two orders of magnitude.}, number={2}, journal={APPLIED PHYSICS LETTERS}, author={Frajtag, P. and El-Masry, N. A. and Nepal, N. and Bedair, S. M.}, year={2011}, month={Jan} }
 @article{frajtag_samberg_el-masry_nepal_bedair_2011, title={Embedded voids formation by overgrowth on GaN nanowires for high-quality GaN films}, volume={322}, ISSN={["0022-0248"]}, DOI={10.1016/j.jcrysgro.2011.02.032}, abstractNote={We report on the epitaxial growth of GaN films on GaN nanowires. GaN nanowires were prepared by the mask-less dry etching technique. The etched, then annealed nanowires form semi-polar and non-polar plane facets with hexagonal symmetry. The different growth rates on the different plane facets result in the formation of void networks. These networks of embedded voids are located near the sapphire substrate, where a high density of dislocations is present. The voids, a few microns in length and a fraction of a micron in diameter, offer free surfaces for dislocation termination, enabling the embedded void approach (EVA) to reduce dislocations. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies show uniform reduction of the dislocation density over large area substrates by about three orders of magnitude and lower surface roughness than the GaN starting material.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Frajtag, P. and Samberg, J. P. and El-Masry, N. A. and Nepal, N. and Bedair, S. M.}, year={2011}, month={May}, pages={27–32} }
 @article{frajtag_hosalli_bradshaw_nepal_el-masry_bedair_2011, title={Improved light-emitting diode performance by conformal overgrowth of multiple quantum wells and fully coalesced p-type GaN on GaN nanowires}, volume={98}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3572032}, DOI={10.1063/1.3572032}, abstractNote={We demonstrate a light-emitting diode (LED) structure with multiple quantum wells (MQWs) conformally grown on semipolar and nonpolar plane facets of n-GaN nanowires (NWs), followed by deposition of fully coalesced p-GaN on these nanowires. Overgrowth on the nanowires’ tips results in inclusion of high density voids, about one micron in height, in the GaN film. The light output intensity of NWs LEDs is more than three times higher than corresponding c-plane LEDs grown simultaneously. We believe this results from a reduced defect density, increased effective area of conformally grown MQWs, absence of polar plane orientation, and improved light extraction.}, number={14}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Frajtag, P. and Hosalli, A. M. and Bradshaw, G. K. and Nepal, N. and El-Masry, N. A. and Bedair, S. M.}, year={2011}, month={Apr}, pages={143104} }
 @article{nepal_frajtag_zavada_el-masry_bedair_wetzel_khan_2011, title={Light emitting diodes based on sidewall m-plane epitaxy of etched GaN/sapphire templates}, volume={8}, ISSN={["1862-6351"]}, DOI={10.1002/pssc.201000983}, abstractNote={Light emitting diodes (LEDs) were grown on the etched m-plane of c-plane GaN/sapphire templates by metal organic chemical vapor deposition (MOCVD). The LEDs, with InxGa1-xN/GaN quantum wells (QWs), were studied and current-voltage measurements show p-n diode behavior. TEM image analysis established that the QWs are on the {101} sidewall semi-polar plane. Electroluminescence measurements on the fabricated LEDs display an emission peak at 487 nm, with a blue shift of only 4 nm on increasing injected current density from 0.3 to 100 A/cm2. The demonstrated sidewall approach significantly reduces the quantum confined Stark Effect found in QWs grown on c-plane substrates (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={7-8}, journal={PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 7-8}, author={Nepal, N. and Frajtag, P. and Zavada, J. M. and El-Masry, N. A. and Bedair, S. M. and Wetzel, C and Khan, A}, year={2011} }
 @article{colter_carlin_samberg_bradshaw_bedair_2011, title={Staggered InGaAs/GaAsP strained layer superlattices for use in optical devices}, volume={208}, ISSN={["1862-6300"]}, DOI={10.1002/pssa.201026624}, abstractNote={Strained layer superlattice (SLS) structures lattice matched to GaAs, such as InGaAs/GaAsP, use thin films to meet both the strain balance and critical layer thickness (CLT) conditions. Optical absorption in the InGaAs layers will be shifted to higher energies relative to thick films due to both the quantum size effect (QSE) and compressive strain, which is an undesirable restriction. We report on a new concept for a strain balance superlattice that will allow for thicker InGaAs films and reduce the cutoff energy. The staggered strain balanced superlattice structure can improve the performance of optical detectors and solar cells.}, number={12}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Colter, P. C. and Carlin, C. Z. and Samberg, J. P. and Bradshaw, G. K. and Bedair, S. M.}, year={2011}, month={Dec}, pages={2884–2888} }
 @article{emar_berkman_zavada_el-masry_bedair_2011, title={Strain relaxation in InxGa1-xN/GaN quantum well structures}, volume={8}, ISSN={1862-6351}, url={http://dx.doi.org/10.1002/pssc.201000984}, DOI={10.1002/pssc.201000984}, abstractNote={We report on the thickness dependence of strain relaxation in InxGa1-xN/GaN for single and multiple quantum-well structures. For InGaN wells thicker than a certain value gradual relaxation occurs and can be presented by two relaxation mechanisms. The first is related to the relaxation of the InGaN well, and the second to the relaxation of the whole multiple quantum well structure. We have also found that the onset of relaxation of multiple quantum wells depends on the number of quantum wells (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={7-8}, journal={physica status solidi (c)}, publisher={Wiley}, author={Emar, Ahmed M. and Berkman, E. Acar and Zavada, J. and El-Masry, Nadia A. and Bedair, S. M.}, year={2011}, month={May}, pages={2034–2037} }
 @article{liliental-weber_ogletree_yu_hawkridge_domagala_bak-misiuk_berman_emara_bedair_2011, title={Structural defects and cathodoluminescence of InxGa1-xN layers}, volume={8}, ISSN={1862-6351}, url={http://dx.doi.org/10.1002/pssc.201001087}, DOI={10.1002/pssc.201001087}, abstractNote={Correlation between structural defects and appearance of multiple cathodoluminescence and photoluminescence peaks of InxGa1-xN grown nominally with x = 0.1 and increasing layer thickness (100 nm to 1000 nm) is discussed. Cathodoluminescence studies were performed on the cross-section samples earlier characterized by electron microscopy including Z-contrast microscopy. Strained and relaxed layers with different In concentrations were observed for InGaN layers above the critical layer thickness. Stacking faults appear at high density in the relaxed layer which also roughens, created a saw-tooth surface profile due to V-shaped pits. Large domains of closely separated stacking faults (polytype-like) were observed. In Z-contrast microscopy stacking faults in upper/lower part of the layer appear with higher/lower brightness, suggesting different amount of In incorporation in agreement with x-ray and RBS results. Only thin, strained InGaN layers showed single band-edge CL peaks. Multiple CL peaks appear in the relaxed, defective portion of the InGaN layers. By comparison with GaN samples where structural defects are associated with CL peak shifts, we postulate that defects, their type and distribution are main contributors to the multiple peaks observed for InGaN samples (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={7-8}, journal={physica status solidi (c)}, publisher={Wiley}, author={Liliental-Weber, Z. and Ogletree, D. F. and Yu, K. M. and Hawkridge, M. and Domagala, J. Z. and Bak-Misiuk, J. and Berman, A. E. and Emara, A. and Bedair, S.}, year={2011}, month={Jun}, pages={2248–2250} }
 @inproceedings{luen_nepal_frajtag_zavada_brown_hommerich_bedair_el masry_2010, title={Ferromagnetism and near infrared luminescence in neodymium and erbium doped gallium nitride via diffusion}, volume={1183}, DOI={10.1557/proc-1183-ff06-01}, booktitle={Novel materials and devices for spintronics}, author={Luen, M. O. and Nepal, N. and Frajtag, P. and Zavada, J. M. and Brown, E. and Hommerich, U. and Bedair, S. M. and El Masry, N. A.}, year={2010}, pages={45–50} }
 @article{hauser_carlin_bedair_2010, title={Modeling of tunnel junctions for high efficiency solar cells}, volume={97}, ISSN={["1077-3118"]}, DOI={10.1063/1.3469942}, abstractNote={Ultrahigh efficiency, in the range of 40%, can be achieved in multijunction solar cells operating at high solar concentrations, larger than 100 suns. Critical to this approach are high band gap tunnel junctions that serve as electrically low loss interconnections between the cells. The purpose of this work is to theoretically model such wide band gap tunnel junctions and to explore the advantages of a staggered band line up for improving the peak tunnel current. Theoretical results are calculated for heterojunction diodes made of n+-InGaP/p+-AlGaAs over a range of doping levels. The results illustrate the advantage of a conduction band discontinuity in achieving low interconnect resistance for multijunction solar cells.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Hauser, John R. and Carlin, Zach and Bedair, S. M.}, year={2010}, month={Jul} }
 @article{nepal_luen_zavada_bedair_frajtag_el-masry_2009, title={Electric field control of room temperature ferromagnetism in III-N dilute magnetic semiconductor films}, volume={94}, ISSN={["1077-3118"]}, DOI={10.1063/1.3110963}, abstractNote={We report on the electrical field control of ferromagnetism (FM) at room temperature in III-N dilute magnetic semiconductor (DMS) films. A GaMnN layer was grown on top of an n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. This FM in GaMnN can be controlled by depletion of the holes in the GaMnN/p-GaN/n-GaN multilayer structures. We have demonstrated the dependence of the FM on the thickness of the p-GaN in this heterostructure and on the applied bias to the GaN p-n junction. The Ms was measured by an alternating gradient magnetometer (AGM) and a strong correlation between the hole concentration near the GaMnN/p-GaN interface and the magnetic properties of the DMS was observed. At room temperature an anomalous Hall effect was measured for zero bias and an ordinary Hall effect for reverse bias in a fully depleted p-GaN layer. This is in close agreement with the AGM measurement results.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Nepal, N. and Luen, M. Oliver and Zavada, J. M. and Bedair, S. M. and Frajtag, P. and El-Masry, N. A.}, year={2009}, month={Mar} }
 @article{liliental-weber_yu_hawkridge_bedair_berman_emara_domagala_bak-misiuk_2009, title={Spontaneous stratification of InGaN layers and its influence on optical properties}, volume={6}, ISSN={1862-6351}, url={http://dx.doi.org/10.1002/pssc.200880985}, DOI={10.1002/pssc.200880985}, abstractNote={Transmission Electron Microscopy, high resolution X-ray diffraction and reciprocal space maps, Rutherford Back Scattering and photoluminescence were applied to study InGaN layers grown by MOCVD with increasing layer thickness (100 nm to 1000 nm) and nominally constant In concentration of 10%. Spontaneous stratification of the layer has been found. A strained layer with lower than nominal In content was found in direct contact with the underlying GaN followed by relaxed layers with a nominal or higher In concentration. A high density of randomly distributed stacking faults as well as domains with cubic structure and closely distributed stacking faults (polytype-like) were present in the thicker layers. Strong corrugation of the thicker sample surface was observed. The appearance of multiple photoluminescence line positions was related not only to the spontaneously formed layers with different In content, but also to the structural planar defects formed in the thicker layers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={S2}, journal={physica status solidi (c)}, publisher={Wiley}, author={Liliental-Weber, Z. and Yu, K.M. and Hawkridge, M. and Bedair, S. and Berman, A.E. and Emara, A. and Domagala, J. and Bak-Misiuk, J.}, year={2009}, month={Mar}, pages={S433–S436} }
 @article{liliental-weber_yu_hawkridge_bedair_berman_emara_khanal_wu_domagala_bak-misiuk_2009, title={Structural perfection of InGaN layers and its relation to photoluminescence}, volume={6}, ISSN={1862-6351 1610-1642}, url={http://dx.doi.org/10.1002/pssc.200982555}, DOI={10.1002/pssc.200982555}, abstractNote={Abstract The relation between structural perfection and optical properties of InGaN with 10% In are discussed. Transmission Electron Microscopy, X‐ray diffraction and Rutherford backscattering spectrometry measurements show that only strained layers with a thickness not exceeding 100 nm are defect free and In concentration is lower than the nominal value. Extension of layer thickness leads to layer sequestration into sublayers with different In contents and the formation of planar defects as a result of layer relaxation. In concentration in such sublayers reach and in some cases exceed the nominal concentration. A single band edge photoluminescence peak is observed only for the thinnest layer. Samples with larger film thickness showed multiple PL peaks corresponding to layers with different In content. Much higher In content would be required to explain the presence of some PL peaks, suggesting that some PL peaks originate from the defective areas of the film. This was confirmed by cathodoluminescence studies performed on the same samples used earlier for TEM studies. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={12}, journal={physica status solidi (c)}, publisher={Wiley}, author={Liliental-Weber, Z. and Yu, K. M. and Hawkridge, M. and Bedair, S. and Berman, A.E. and Emara, A. and Khanal, D. R. and Wu, J. and Domagala, J. and Bak-Misiuk, J.}, year={2009}, month={Dec}, pages={2626–2631} }
 @article{berkman_el-masry_emara_bedair_2008, title={Nearly lattice-matched n, i, and p layers for InGaN p-i-n photodiodes in the 365-500 nm spectral range}, volume={92}, ISSN={["0003-6951"]}, DOI={10.1063/1.2896648}, abstractNote={We report on nearly lattice-matched grown InGaN based p-i-n photodiodes detecting in the 365–500nm range with tunable peak responsivity tailored by the i-layer properties. The growth of lattice matched i- and n-InGaN layer leads to improvement in the device performance. This approach produced photodiodes with zero-bias responsivities up to 0.037A∕W at 426nm, corresponding to 15.5% internal quantum efficiency. The peak responsivity wavelength ranged between 416 and 466nm, the longest reported for III-N photodiodes. The effects of InN content and i-layer thickness on photodiode properties and performance are discussed.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Berkman, E. A. and El-Masry, N. A. and Emara, A. and Bedair, S. M.}, year={2008}, month={Mar} }
 @article{nepal_bedair_el-masry_lee_steckl_zavada_2007, title={Correlation between compositional fluctuation and magnetic properties of Tm-doped AlGaN alloys}, volume={91}, ISSN={["1077-3118"]}, DOI={10.1063/1.2817741}, abstractNote={The magnetic properties of Tm-doped AlxGa1−xN (0⩽x⩽1) alloys grown by solid-source molecular beam epitaxy were studied by hysteresis measurements and shown to exhibit ferromagnetic behavior at room temperature. The measured magnetization was strongly dependent on the Al content and reached a maximum for x=0.62. Previously reported photoluminescence measurements on these films yielded a blue emission at 465nm with peak intensity at the same Al content. Both magnetic and optical properties are directly correlated with the alloy compositional fluctuation found in undoped AlxGa1−xN alloys.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Nepal, N. and Bedair, S. M. and El-Masry, N. A. and Lee, D. S. and Steckl, A. J. and Zavada, J. M.}, year={2007}, month={Nov} }
 @article{nepal_mahros_bedair_el-masry_zavada_2007, title={Correlation between photoluminescence and magnetic properties of GaMnN films}, volume={91}, ISSN={["1077-3118"]}, DOI={10.1063/1.2823602}, abstractNote={Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation N. Nepal, Amr M. Mahros, S. M. Bedair, N. A. El-Masry, J. M. Zavada; Correlation between photoluminescence and magnetic properties of GaMnN films. Appl. Phys. Lett. 10 December 2007; 91 (24): 242502. https://doi.org/10.1063/1.2823602 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioApplied Physics Letters Search Advanced Search |Citation Search}, number={24}, journal={APPLIED PHYSICS LETTERS}, author={Nepal, N. and Mahros, Amr M. and Bedair, S. M. and El-Masry, N. A. and Zavada, J. M.}, year={2007}, month={Dec} }
 @article{barletta_berkman_moody_el-masry_emara_reed_bedair_2007, title={Development of green, yellow, and amber light emitting diodes using InGaN multiple quantum well structures}, volume={90}, ISSN={["0003-6951"]}, DOI={10.1063/1.2721133}, abstractNote={The authors present optical and electrical data for long wavelength (573–601nm) InGaN∕GaN multiple quantum well light emitting diodes (LEDs) grown by metal organic chemical vapor deposition. These results are achieved by optimizing the active layer growth temperature and the quantum well width. Also, the p-GaN is grown at low temperature to avoid the disintegration of the InGaN quantum wells with high InN content. A redshift is observed for both the green and yellow LEDs upon decreasing the injection current at low current regime. In the case of the yellow LED, this shift is enough to push emission into the amber (601nm).}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Barletta, Philip T. and Berkman, E. Acar and Moody, Baxter F. and El-Masry, Nadia A. and Emara, Ahmed M. and Reed, Mason J. and Bedair, S. M.}, year={2007}, month={Apr} }
 @article{mahros_luen_emara_bedair_berkman_el-masry_zavada_2007, title={Magnetic and magnetotransport properties of (AlGaN/GaN): Mg/(GaMnN) heterostructures at room temperature}, volume={90}, ISSN={["0003-6951"]}, DOI={10.1063/1.2749717}, abstractNote={Dilute magnetic semiconductor films (GaMnN) are highly resistive, making transport measurements difficult to achieve. However, when GaMnN films are sandwiched between p-type doped (AlGaN∕GaN) strained-layer superlattices, holes from the superlattice interact with the Mn3+∕2+ ions and transport measurements were realized. The authors have found also that the ferromagnetic properties of GaMnN critically depend on the level of p-type doping in the superlattice. They report anomalous Hall effect measurements in this (AlGaN∕GaN):Mg∕(GaMnN) multilayered structure. The current results also demonstrate the role of carriers, especially holes, in mediating the ferromagnetic properties of GaMnN dilute magnetic semiconductor films.}, number={25}, journal={APPLIED PHYSICS LETTERS}, author={Mahros, Amr M. and Luen, M. O. and Emara, A. and Bedair, S. M. and Berkman, E. A. and El-Masry, N. A. and Zavada, J. M.}, year={2007}, month={Jun} }
 @misc{zhang_misra_bedair_ozturk_2007, title={Optoelectonic devices having arrays of quantum-dot compound semiconductor superlattices therein}, volume={7,265,375}, number={2007 Sept. 4}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Zhang, Z.-B. and Misra, V. and Bedair, S. M. A. and Ozturk, M.}, year={2007} }
 @article{reed_arkun_berkman_elmasry_zavada_luen_reed_bedair_2005, title={Effect of doping on the magnetic properties of GaMnN: Fermi level engineering}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1881786}, abstractNote={GaMnN dilute magnetic semiconductor samples, prepared by metalorganic chemical vapor deposition, are shown to exhibit ferromagnetism or even paramagnetism depending upon the type and concentration of extrinsic impurity present in the film. In addition, GaMnN deposited using growth parameters normally yielding a nonferromagnetic film becomes strongly ferromagnetic with the addition of magnesium, an acceptor dopant. Based upon these observations, it seems that ferromagnetism in this material system depends on the relative position of the Mn energy band and the Fermi level within the GaMnN band gap. Only when the Fermi level closely coincides with the Mn-energy level is ferromagnetism achieved. By actively engineering the Fermi energy to be within or near the Mn energy band, room temperature ferromagnetism is realized.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Reed, MJ and Arkun, FE and Berkman, EA and Elmasry, NA and Zavada, J and Luen, MO and Reed, ML and Bedair, SM}, year={2005}, month={Mar} }
 @article{elmasry_hunter_elnaggar_bedair_2005, title={Five-nanometer thick silicon on insulator layer}, volume={98}, ISSN={["0021-8979"]}, DOI={10.1063/1.1803625}, abstractNote={Silicon on insulator (SOI) has been achieved using epitaxially grown Si∕Y2O3∕Si structure. Silicon film as thin as 5nm was achieved. Pulsed laser deposition technique was used for the epitaxial deposition of both the Y2O3 and silicon. The growth conditions were adjusted to achieve two-dimensional growths of single crystal silicon films on Y2O3. No dislocations were observed in these silicon epitaxial films. This approach will allow the independent thickness control of both silicon and the oxide in the nanometer range. Si∕CeO2∕Si SOI structure was not as successful due to the formation of an amorphous oxide film at the interfaces.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Elmasry, NA and Hunter, M and ElNaggar, A and Bedair, SM}, year={2005}, month={Nov} }
 @article{reed_reed_luen_berkman_arkun_bedair_zavada_el-masry_2005, title={Magnetic properties of Mn-doped GaN andp-i-n junctions}, volume={2}, ISSN={1610-1634 1610-1642}, url={http://dx.doi.org/10.1002/pssc.200461517}, DOI={10.1002/pssc.200461517}, abstractNote={We report on the growth and magnetic properties of GaMnN films and p-i-n junctions grown by metal-organic chemical vapor deposition. The magnetic properties of MOCVD grown GaMnN were found to depend upon the type and concentration of the co-dopant. Si or Mg co-doping of GaMnN films led to either ferromagnetic or paramagnetic behavior depending on the concentration. The magnetic properties within the GaMnN material system appear to correlate with the position of the Fermi level. Ferromagnetism was observed only when the Fermi energy level was within or very close to the Mn energy band. The presence of the Fermi energy level within the Mn energy band allows the presence of carriers that mediate ferromagnetism. These results further confirm that the ferromagnetic properties result from a solid solution of Mn in the GaN. Mn-doped GaN p-i-n junctions which were grown to study the effect of the magnetic properties on the I/V characteristics. These devices consist of GaN:Si/GaMnN/GaN:Mg layers grown by metal-organic chemical vapor deposition. The carrier concentrations for the n and p-type layers are ∼5 × 1018/cm3 and 1 × 1018/cm3 respectively, where the GaMnN i layer is approximately 0.2–0.45 µm thick with up to 0.5% Mn. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={7}, journal={physica status solidi (c)}, publisher={Wiley}, author={Reed, M.L. and Reed, M.J. and Luen, M.O. and Berkman, E.A. and Arkun, F.E. and Bedair, S.M. and Zavada, J.M. and El-Masry, N. A.}, year={2005}, month={May}, pages={2403–2406} }
 @misc{zhang_misra_bedair_ozturk_2005, title={Optoelectronic devices having arrays of quantum-dot compound semiconductor superlattices therein}, volume={6,914,256}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Zhang, Z. and Misra, V. and Bedair, S. M. A. and Ozturk, M.}, year={2005} }
 @article{arkun_reed_berkman_el-masry_zavada_reed_bedair_2004, title={Dependence of ferromagnetic properties on carrier transfer at GaMnN/GaN : Mg interface}, volume={85}, ISSN={["1077-3118"]}, DOI={10.1063/1.1810216}, abstractNote={We report on the dependence of ferromagnetic properties of metalorganic chemical vapor deposition grown GaMnN films on carrier transfer across adjacent layers. We found that the magnetic properties of GaMnN, as a part of GaMnN∕GaN:Mg heterostructures, depend on the thickness of both the GaMnN film and the adjacent GaN:Mg layer and on the presence of a wide band gap barrier at this interface. These results are explained based on the occupancy of the Mn energy band and how the occupancy can be altered due to carrier transfer at the GaMnN∕GaN:Mg interfaces.}, number={17}, journal={APPLIED PHYSICS LETTERS}, author={Arkun, FE and Reed, MJ and Berkman, EA and El-Masry, NA and Zavada, JM and Reed, ML and Bedair, SM}, year={2004}, month={Oct}, pages={3809–3811} }
 @article{xiao_kim_bedair_zavada_2004, title={Design of white light-emitting diodes using InGaN/AlInGaN quantum-well structures}, volume={84}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1644920}, DOI={10.1063/1.1644920}, abstractNote={Based on the Rashba–Sheka–Pikus Hamiltonian in the vicinity of the Γ point, and taking into consideration spontaneous and piezoelectric polarization, the optical intensity of nitride-based quantum-well light-emitting diodes has been calculated. It is found that strain substantially alters the subband structure and thus the output intensity of these nitride-biased quantum-well light-emitting diodes. A design that uses AlInGaN as the quantum barrier is proposed to realize efficient red emission, which is hard to achieve if GaN is used as the barrier. In the proposed design, three different InGaN/AlInGaN quantum-well structures emit red, green, and blue light of similar intensity. Also, to achieve high efficiency, important factors related to the oscillator strength are discussed in detail.}, number={5}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Xiao, D. and Kim, K. W. and Bedair, S. M. and Zavada, J. M.}, year={2004}, month={Feb}, pages={672–674} }
 @article{reed_reed_jagannadham_verghese_bedair_el-masry_butler_2004, title={Electrical characterization of B-10 doped diamond irradiated with low thermal neutron fluence}, volume={22}, ISSN={["1520-8559"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-4344661941&partnerID=MN8TOARS}, DOI={10.1116/1.1763910}, abstractNote={A sample of B10 isotope doped diamond was neutron irradiated to a thermal fluence of 1.3×1019 neutron cm−2. The diamond sample was cooled continuously during irradiation in a nuclear reactor. Li7 is formed by nuclear transmutation reaction from B10. Characterization for electrical conductance in the temperature range of 160 K<T<600 K was performed on an unirradiated B10 doped sample and the B10 doped and irradiated sample. The unirradiated diamond sample showed p-type conductance at higher temperature (T>200 K) and p-type surface conductance at lower temperature (T<200 K). The irradiated sample showed decreasing conductance below 230 K and increasing conductance above 230 K with increasing temperature. Furthermore, the conductance showed a decrease above 400 K followed by an increase above 500 K. The observed behavior below 400 K with increase in temperature is interpreted in terms of compensation of surface p-type carriers by n-type bulk carriers generated from Li7 that is formed by nuclear transmutation reaction from B10 atoms. Also, compensation of n-type carriers from Li7 by p-type carriers from B10 is used to interpret the conductance above 400 K. A low concentration of radiation induced defects, absence of defect complexes, and the low activation energy of n-type Li7 are thought responsible for the observed variation of conductance in the irradiated diamond. The present results illustrate that neutron transmutation from B10 doped diamond is a useful method to achieve n-type conductivity in diamond.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Reed, ML and Reed, MJ and Jagannadham, K and Verghese, K and Bedair, SM and El-Masry, N and Butler, JE}, year={2004}, pages={1191–1194} }
 @misc{zhang_misra_bedair_ozturk_2004, title={Methods of forming nano-scale electronic and optoelectronic devices using non-photolithographically defined nano-channel templates}, volume={6,709,929}, number={2004 Mar. 23}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Zhang, Z. and Misra, V. and Bedair, S. M. A. and Ozturk, M.}, year={2004} }
 @article{moody_barletta_el-masry_roberts_aumer_leboeuf_bedair_2002, title={Effect of H-2 on nitrogen incorporation in the metalorganic chemical vapor deposition of GaAs1-yNy (0 <= y <= 0.08)}, volume={80}, ISSN={["0003-6951"]}, DOI={10.1063/1.1464225}, abstractNote={The effect of hydrogen on the incorporation of nitrogen in GaAs1−yNy grown by metalorganic chemical vapor deposition (MOCVD) is reported. Nitrogen content as high as y=0.081 has been achieved when the use of H2 is completely avoided in the MOCVD growth of GaAs1−yNy. When H2 is added to the growth ambient, the value of y in GaAs1−yNy decreases as the relative percent of H2 in the carrier gas increases. We will report on the properties of these GaAsN films and discuss the nature of the effect that H2 has on modulating the N content in these films.}, number={14}, journal={APPLIED PHYSICS LETTERS}, author={Moody, BF and Barletta, PT and El-Masry, NA and Roberts, JC and Aumer, ME and LeBoeuf, SF and Bedair, SM}, year={2002}, month={Apr}, pages={2475–2477} }
 @article{aumer_leboeuf_moody_bedair_nam_lin_jiang_2002, title={Effects of tensile, compressive, and zero strain on localized states in AlInGaN/InGaN quantum-well structures}, volume={80}, ISSN={["0003-6951"]}, DOI={10.1063/1.1469219}, abstractNote={The recombination dynamics of optical transitions as well as strain effects in AlInGaN/In0.08Ga0.92N quantum wells (QWs) were studied. QW emission energy, photoluminescence decay behavior, photoluminescence emission line shape, and nonradiative recombination behavior were found to be strong functions of strain as well as localization. The degree of carrier localization was inferred by modeling several aspects of optical behavior obtained from variable temperature time-resolved photoluminescence experiments. According to the modeling results, the degree of localization was found to be a minimum for unstrained QWs and increased as either tensile or compressive strain increased, indicating that InGaN QW microstructure is a function of the lattice-mismatch-induced strain experienced during deposition.}, number={17}, journal={APPLIED PHYSICS LETTERS}, author={Aumer, ME and LeBoeuf, SF and Moody, BF and Bedair, SM and Nam, K and Lin, JY and Jiang, HX}, year={2002}, month={Apr}, pages={3099–3101} }
 @misc{roberts_parker_muth_leboeuf_aumer_bedair_reed_2002, title={Ultraviolet-visible metal-semiconductor-metal photodetectors fabricated from InxGa1-xN (0 <= x <= 0.13)}, volume={31}, number={1}, journal={Journal of Electronic Materials}, author={Roberts, J. C. and Parker, C. A. and Muth, J. F. and Leboeuf, S. F. and Aumer, M. E. and Bedair, S. M. and Reed, M. J.}, year={2002}, month={Jan}, pages={L1–6} }
 @article{liliental-weber_benamara_washburn_domagala_bak-misiuk_piner_roberts_bedair_2001, title={Relaxation of InGaN thin layers observed by x-ray and transmission electron microscopy studies}, volume={30}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-001-0056-5}, number={4}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Liliental-Weber, Z and Benamara, M and Washburn, J and Domagala, JZ and Bak-Misiuk, J and Piner, EL and Roberts, JC and Bedair, SM}, year={2001}, month={Apr}, pages={439–444} }
 @article{reed_el-masry_stadelmaier_ritums_reed_parker_roberts_bedair_2001, title={Room temperature ferromagnetic properties of (Ga, Mn)N}, volume={79}, ISSN={["1077-3118"]}, DOI={10.1063/1.1419231}, abstractNote={Dilute magnetic semiconductor GaN with a Curie temperature above room temperature has been achieved by manganese doping. By varying the growth and annealing conditions of Mn-doped GaN we have identified Curie temperatures in the range of 228–370 K. These Mn-doped GaN films have ferromagnetic behavior with hysteresis curves showing a coercivity of 100–500 Oe. Structure characterization by x-ray diffraction and transmission electron microscopy indicated that the ferromagnetic properties are not a result of secondary magnetic phases.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Reed, ML and El-Masry, NA and Stadelmaier, HH and Ritums, MK and Reed, MJ and Parker, CA and Roberts, JC and Bedair, SM}, year={2001}, month={Nov}, pages={3473–3475} }
 @article{reed_ritums_stadelmaier_reed_parker_bedair_el-masry_2001, title={Room temperature magnetic (Ga,Mn)N: a new material for spin electronic devices}, volume={51}, ISSN={["0167-577X"]}, DOI={10.1016/S0167-577X(01)00342-1}, abstractNote={A new dilute magnetic semiconductor (Ga,Mn)N grown by metal organic chemical vapor deposition (MOCVD) is reported. Vibrating sample magnetometer (VSM) and extraordinary Hall effect (EHE) measurements verified a ferromagnetic component at room temperature. The direction of the easy axis and the Curie temperature varies with the growth conditions, the latter ranging from 38°C to 75°C. Secondary ion mass spectroscopy (SIMS) confirms diffusion of Mn into the GaN to a depth of 380 A.}, number={6}, journal={MATERIALS LETTERS}, author={Reed, ML and Ritums, MK and Stadelmaier, HH and Reed, MJ and Parker, CA and Bedair, SM and El-Masry, NA}, year={2001}, month={Dec}, pages={500–503} }
 @article{el-masry_behbehani_leboeuf_aumer_roberts_bedair_2001, title={Self-assembled AlInGaN quaternary superlattice structures}, volume={79}, ISSN={["0003-6951"]}, DOI={10.1063/1.1400763}, abstractNote={When an AlInGaN quaternary alloy is grown by metalorganic chemical-vapor deposition under certain growth conditions, a self-assembled superlattice structure is obtained. The superlattice structure is made of quaternary layers with different AIN and InN compositions. Transmission electron microscopy data show that the superlattice periodicity is regular with an individual layer thickness that depends on the growth conditions. Secondary ion mass spectrometry measurements show that the layers’ composition alternate between high-AIN and InN content and low-AlN and-InN content, while the in-plane lattice constant remains constant for both layers. A model is presented as a preliminary effort to explain these results.}, number={11}, journal={APPLIED PHYSICS LETTERS}, author={El-Masry, NA and Behbehani, MK and LeBoeuf, SF and Aumer, ME and Roberts, JC and Bedair, SM}, year={2001}, month={Sep}, pages={1616–1618} }
 @article{aumer_leboeuf_moody_bedair_2001, title={Strain-induced piezoelectric field effects on light emission energy and intensity from AlInGaN/InGaN quantum wells}, volume={79}, ISSN={["1077-3118"]}, DOI={10.1063/1.1418453}, abstractNote={We report on the effects of the piezoelectric field and well width on the transition energy and intensity for InGaN quantum well structures with GaN or AlInGaN quaternary barriers. It was found that the emission energy of compressively strained GaN/In0.08Ga0.92N quantum wells exhibits a strong well width dependence not accounted for by quantum confinement subband energy shifting alone. However, for unstrained quantum well layers with quaternary barriers, no emission energy dependence on width was observed due to the elimination of the piezoelectric field, which was measured to be at least 0.6 MV/cm for the strained quantum wells. Furthermore, the unstrained quantum wells demonstrated a higher intensity than their strained counterparts for all quantum well widths investigated. The current data will help clarify the origin of emission in InGaN quantum wells.}, number={23}, journal={APPLIED PHYSICS LETTERS}, author={Aumer, ME and LeBoeuf, SF and Moody, BF and Bedair, SM}, year={2001}, month={Dec}, pages={3803–3805} }
 @article{alexson_bergman_nemanich_dutta_stroscio_parker_bedair_el-masry_adar_2001, title={Ultraviolet raman study of A(1)(LO) and E-2 phonons in InxGa1-xN alloys}, volume={89}, ISSN={["0021-8979"]}, DOI={10.1063/1.1330760}, abstractNote={Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Dimitri Alexson, Leah Bergman, Robert J. Nemanich, Mitra Dutta, Michael A. Stroscio, C. A. Parker, S. M. Bedair, N. A. El-Masry, Fran Adar; Ultraviolet Raman study of A1(LO) and E2 phonons in InxGa1−xN alloys. Journal of Applied Physics 1 January 2001; 89 (1): 798–800. https://doi.org/10.1063/1.1330760 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioJournal of Applied Physics Search Advanced Search |Citation Search}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Alexson, D and Bergman, L and Nemanich, RJ and Dutta, M and Stroscio, MA and Parker, CA and Bedair, SM and El-Masry, NA and Adar, F}, year={2001}, month={Jan}, pages={798–800} }
 @article{reed_el-masry_parker_roberts_bedair_2000, title={Critical layer thickness determination of GaN/InGaN/GaN double heterostructures}, volume={77}, DOI={10.1063/1.1334361}, abstractNote={We report on the critical layer thickness of GaN/InxGa1−xN/GaN double heterostructures in the composition range 0<x<0.16. The evolution of the photoluminescence spectra and the electrical properties of the InxGa1−xN well were monitored as its thickness was increased for a given % InN. Due to compressive stress and possible quantum-size effects, the emission energy from thin InGaN wells is blueshifted relative to thicker wells of a given % InN. The transition from the blueshifted emission of strained InGaN to redshifted emission of relaxed InGaN is also accompanied by dramatic changes in film conductivity and mobility. The thickness at which the onset of relaxation occurs is deemed the critical layer thickness of the InxGa1−xN film.}, number={25}, journal={Applied Physics Letters}, author={Reed, M. J. and El-Masry, N. A. and Parker, C. A. and Roberts, J. C. and Bedair, S. M.}, year={2000}, pages={4121–4123} }
 @article{aumer_leboeuf_bedair_smith_lin_jiang_2000, title={Effects of tensile and compressive strain on the luminescence properties of AlInGaN/InGaN quantum well structures}, volume={77}, ISSN={["0003-6951"]}, DOI={10.1063/1.1306648}, abstractNote={We report on the luminescence properties of AlInGaN/In0.08Ga0.92N quantum wells (QWs) subjected to a variable amount of lattice mismatch induced strain, including wells with zero strain, compressive strain, and tensile strain. The primary peak emission energy of a 3 nm In0.08Ga0.92N QW was redshifted by 236 meV as the stress in the well was changed from −0.86% (compressive) to 0.25% (tensile). It was also found that the photoluminescence intensity of quantum wells decreased with increasing strain. A lattice matched 9 nm QW exhibited a luminescence intensity that is three times greater than its highly strained counterpart. The potential applications of this strain engineering will be discussed.}, number={6}, journal={APPLIED PHYSICS LETTERS}, author={Aumer, ME and LeBoeuf, SF and Bedair, SM and Smith, M and Lin, JY and Jiang, HX}, year={2000}, month={Aug}, pages={821–823} }
 @article{hunter_reed_el-masry_roberts_bedair_2000, title={Epitaxial Y2O3 films grown on Si(111) by pulsed-laser ablation}, volume={76}, ISSN={["0003-6951"]}, DOI={10.1063/1.126217}, abstractNote={Y2O3 has a relatively high dielectric constant (13–17) leading to several potential applications. In this work, pulsed-laser deposition was used to grow epitaxial Y2O3 films on Si(111) substrates. Structural characterization indicated two-dimensional growth without the formation of an amorphous interfacial layer. Annealing in either Ar or O2 was found to induce an O2 diffusion reaction resulting in the formation of two interfacial amorphous layers. Electrical characterization by capacitance–voltage and current–voltage indicated that the as-grown samples were poor insulating films. Annealing the samples improved the electrical performance by lowering leakage currents and exhibiting inversion during capacitance–voltage testing. This epitaxial growth points toward the possibility of the heteroepitaxial growth of silicon on insulator device structures.}, number={14}, journal={APPLIED PHYSICS LETTERS}, author={Hunter, ME and Reed, MJ and El-Masry, NA and Roberts, JC and Bedair, SM}, year={2000}, month={Apr}, pages={1935–1937} }
 @article{leboeuf_aumer_bedair_2000, title={Exploring the effects of tensile and compressive strain on two-dimensional electron gas properties within InGaN quantum wells}, volume={77}, ISSN={["0003-6951"]}, DOI={10.1063/1.126889}, abstractNote={With the advent of high-quality AllnGaN quaternary cladding, InGaN quantum wells (QWs) have now been studied under both compressive and tensile strain, as well as no strain at all! This has allowed the experimental investigation of the two-dimensional electron gas (2DEG) properties within InGaN QWs that have been subjected to a full range of strain, opening the doors to a new realm of strain engineering. We present the capacitance–voltage-derived 2DEG properties of several In0.08Ga0.92N QWs subject to various degrees of strain. Strained In0.08Ga0.92N QWs clad with GaN exhibit better 2DEG confinement than their unstrained Al0.24In0.09Ga0.67N-clad counterparts. For the case of compressive-strained QWs, it was found that the peak 2DEG concentration increases linearly with well width. In contrast, such dependence was not observed for the case of unstrained QWs with lattice-matched cladding. Of further interest, the 2DEGs for compressive and tensile In0.08Ga0.92N QWs are localized at opposite interfaces, which is attributed to strain-induced piezoelectric fields pointing in opposite directions.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={LeBoeuf, SF and Aumer, ME and Bedair, SM}, year={2000}, month={Jul}, pages={97–99} }
 @article{liu_bedair_el-masry_2000, title={Mn-prelayer effects on the epitaxial growth of MnSb on (111)B GaAs by pulsed laser deposition}, volume={42}, ISSN={["0167-577X"]}, DOI={10.1016/s0167-577x(99)00170-6}, abstractNote={Ferromagnetic thin films of MnSb have been grown epitaxially on (111)B GaAs substrate by pulsed laser deposition. The epitaxial growth was achieved by either depositing Mn/Sb multilayers or direct ablation of a Mn50Sb50 alloy target. The epitaxial growth occurs with (0001) of the MnSb film parallel to (111) of GaAs, with [011̄1] of MnSb 4° off [200] of the GaAs substrate, as determined from selected area diffraction (SAD). The easy magnetization in these films lies in the basal plane with coercivities, which vary from 40 to 110 Oe measured by Vibrating Sample Magnetometry (VSM). A Mn prelayer was important for high quality MnSb epitaxial growth with the c-axis perpendicular to the substrate surface. Films with an Sb prelayer or without Mn as a prelayer resulted in polycrystalline growth of MnSb. The mechanism of how the Mn prelayer facilitates the MnSb epitaxial growth is discussed in terms of two models.}, number={1-2}, journal={MATERIALS LETTERS}, author={Liu, SX and Bedair, SM and El-Masry, NA}, year={2000}, month={Jan}, pages={121–129} }
 @article{reed_liu_roberts_stadelmaier_bedair_el-masry_2000, title={The planar Hall effect in MnSb films and MnSb-based multilayer structures grown on (111)B GaAs}, volume={218}, ISSN={["0304-8853"]}, DOI={10.1016/S0304-8853(00)00403-0}, abstractNote={We report on the planar Hall effect properties of ferromagnetic MnSb films in ferromagnetic/nonmagnetic multilayer structures. We demonstrate an enhancement of the relative planar Hall resistivity when MnSb is used in multilayer structures. In single-layer MnSb films, the relative planar Hall resistivity is ∼2.5%, while the multilayer structures demonstrate up to ∼41% change. The following structures were prepared by pulsed laser deposition and grown on (1 1 1)B GaAs: epitaxial and polycrystalline MnSb thin films, MnSb/Bi multilayers and Mn/Sb/Mn/Bi multilayers. The multilayer structures also demonstrate temperature dependence, as the relative resistivity decreases to ∼30% when the temperature decreases to 100 K.}, number={2-3}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Reed, ML and Liu, SX and Roberts, JC and Stadelmaier, HH and Bedair, SM and El-Masry, NA}, year={2000}, month={Aug}, pages={177–181} }
 @article{parker_roberts_bedair_reed_liu_el-masry_1999, title={Determination of the critical layer thickness in the InGaN/GaN heterostructures}, volume={75}, ISSN={["0003-6951"]}, DOI={10.1063/1.125146}, abstractNote={We present an approach to determine the critical layer thickness in the InxGa1−xN/GaN heterostructure based on the observed change in the photoluminescence emission as the InxGa1−xN film thickness increases. From the photoluminescence data, we identify the critical layer thickness as the thickness where a transition occurs from the strained to unstrained condition, which is accompanied by the appearance of deep level emission and a drop in band edge photoluminescence intensity. The optical data that indicate the onset of critical layer thickness, was also confirmed by the changes in InxGa1−xN surface morphology with thickness, and is consistent with x-ray diffraction measurements.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Parker, CA and Roberts, JC and Bedair, SM and Reed, MJ and Liu, SX and El-Masry, NA}, year={1999}, month={Nov}, pages={2776–2778} }
 @article{joshkin_parker_bedair_muth_shmagin_kolbas_piner_molnar_1999, title={Effect of growth temperature on point defect density of unintentionally doped GaN grown by metalorganic chemical vapor deposition and hydride vapor phase epitaxy}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.370727}, abstractNote={We report on the investigation of the effect of growth temperature on point defect density of unintentionally doped GaN grown by atmospheric pressure metalorganic chemical vapor deposition and hydride vapor phase epitaxy. A correlation between photoluminescence (PL) spectra and the concentration of donors and acceptors in unintentionally doped GaN is presented. The effects of oxygen and native acceptors on the electrical and optical properties of GaN epitaxial layers are discussed and a classification of PL data is presented. On this basis we show that oxygen creates a shallow donor in GaN with an activation energy of about 23.5±1 meV. We determine that the concentration of native acceptors in GaN increases with an increase in growth temperature. These native acceptors, probably gallium antisites (GaN) and/or gallium vacancies (VGa), are nonradiative defects. We show that a second donor level in GaN has an activation energy of about 52.5±2.5 meV and produces a PL peak with an energy of about 3.45 eV at low temperatures. From Hall investigations we show that a third donor in GaN has an activation energy of 110±10 meV.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Joshkin, VA and Parker, CA and Bedair, SM and Muth, JF and Shmagin, IK and Kolbas, RM and Piner, EL and Molnar, RJ}, year={1999}, month={Jul}, pages={281–288} }
 @article{aumer_leboeuf_mcintosh_bedair_1999, title={High optical quality AlInGaN by metalorganic chemical vapor deposition}, volume={75}, ISSN={["0003-6951"]}, DOI={10.1063/1.125336}, abstractNote={We report on the metalorganic chemical vapor deposition of the quaternary alloy AlInGaN. We found it desirable to grow quaternary films at temperatures greater than 855 °C in order to suppress deep level emissions in the room-temperature photoluminescence. Details of the conditions necessary to grow In0.1Ga0.9N at 875 °C are presented. Strained and relaxed AlInGaN films were grown with good optical and structural properties for AlN compositions up to 26% and InN content up to 11%. The effects of strain were observed by a difference in the band gap between thin and thick films with the same compositions. The potential impact of the use of quaternary films is discussed regarding strain engineering for the improvement of present device designs.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Aumer, ME and LeBoeuf, SF and McIntosh, FG and Bedair, SM}, year={1999}, month={Nov}, pages={3315–3317} }
 @article{robins_paul_parker_roberts_bedair_piner_el-masry_1999, title={Optical absorption, Raman, and photoluminescence excitation spectroscopy of inhomogeneous InGaN films}, volume={4S1}, DOI={10.1557/s1092578300002490}, abstractNote={In x Ga 1−x N films with x=0.06 to x=0.49 were characterized by optical transmittance, Raman, and photoluminescence excitation spectroscopies. Previous microstructural characterizations detected phase separation only in films with x>0.2. The transmittance data suggest that compositional inhomogeneity is also present in the lower-x films (x<0.2). Both Raman and photoluminescence excitation spectra show features that correlate with compositional inhomogeneity and phase separation in the films with x>0.2. The composition dependence of the Raman spectra, from x=0.28 to x=0.49, is consistent with an increase in the size of the phase-separated regions with increasing x.}, number={G3.22}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Robins, L. H. and Paul, A. J. and Parker, C. A. and Roberts, J. C. and Bedair, S. M. and Piner, E. L. and El-Masry, N. A.}, year={1999} }
 @article{parker_roberts_bedair_reed_liu_el-masry_robins_1999, title={Optical band gap dependence on composition and thickness of InxGa1-xN (0 < x < 0.25) grown on GaN}, volume={75}, ISSN={["1077-3118"]}, DOI={10.1063/1.125079}, abstractNote={Band gap measurements have been carried out in strained and relaxed InxGa1−xN epilayers with x<0.25. Values of x were determined from x-ray diffraction of relaxed films. The lowest energy absorption threshold, measured by transmittance, was found to occur at the same energy as the peak of the photoluminescence spectrum. Bowing parameters for both strained and relaxed films were determined to be 3.42 and 4.11 eV, respectively. The dependence of the band gap shift, ΔEg, on strain is presented.}, number={17}, journal={APPLIED PHYSICS LETTERS}, author={Parker, CA and Roberts, JC and Bedair, SM and Reed, MJ and Liu, SX and El-Masry, NA and Robins, LH}, year={1999}, month={Oct}, pages={2566–2568} }
 @article{behbehani_piner_liu_el-masry_bedair_1999, title={Phase separation and ordering coexisting in InxGa1-xN grown by metal organic chemical vapor deposition}, volume={75}, ISSN={["0003-6951"]}, DOI={10.1063/1.124964}, abstractNote={We have recently reported the occurrence of phase separation in InxGa1−xN samples with x>0.25. Theoretical studies have suggested that InxGa1−xN can phase-separate asymmetrically into a low InN% phase and an ordered high InN% phase. In this letter, we report on the existence of simultaneous phase separation and ordering of InxGa1−xN samples with x>0.25. In these samples, phase separation was detected by both transmission electron microscopy selected area diffraction (TEM-SAD) and x-ray diffraction. Ordering was detected by both imaging and TEM-SAD.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Behbehani, MK and Piner, EL and Liu, SX and El-Masry, NA and Bedair, SM}, year={1999}, month={Oct}, pages={2202–2204} }
 @article{joshkin_parker_bedair_krasnobaev_cuomo_davis_suvkhanov_1998, title={Fine structure of near-band-edge photoluminescence in He+-irradiated GaN grown on SiC}, volume={72}, ISSN={["0003-6951"]}, DOI={10.1063/1.121474}, abstractNote={The effect of He ion implantation on the optical properties of epitaxial GaN-on-SiC was studied. We observed that He+ irradiation increases the relative intensity of the “blue emission” and resistivity of GaN films and decreases the intensity of the near-band-edge photoluminescence. Because the intensity of the main peak is drastically decreased, the fine structure of the near-band-edge photoluminescence in GaN after He+ irradiation was observed. From a comparison of observed sharp lines with photoluminescence peaks of GaN doped with oxygen, we conclude that oxygen can produce a complex, which is characterized by a strong localization of free carriers and a large lattice distortion. The zero-phonon line of this defect has energy close to the band-gap energy of GaN.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Joshkin, VA and Parker, CA and Bedair, SM and Krasnobaev, LY and Cuomo, JJ and Davis, RF and Suvkhanov, A}, year={1998}, month={Jun}, pages={2838–2840} }
 @misc{mcintosh_bedair_el-masry_roberts_1998, title={Methods of forming indium gallium nitride or aluminum indium gallium nitride using controlled hydrogen gas flow}, volume={5,851,905}, number={1998 Dec. 22}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={McIntosh, F. G. and Bedair, S. M. and El-Masry, N. A. and Roberts, J. C.}, year={1998}, month={Dec} }
 @article{el-masry_piner_liu_bedair_1998, title={Phase separation in InGaN grown by metalorganic chemical vapor deposition}, volume={72}, ISSN={["0003-6951"]}, DOI={10.1063/1.120639}, abstractNote={We report on phase separation in thick InGaN films with up to 50% InN grown by metalorganic chemical vapor deposition from 690 to 780 °C. InGaN films with thicknesses of 0.5 μm were analyzed by θ–2θ x-ray diffraction, transmission electron microscopy (TEM), and selected area diffraction (SAD). Single phase InGaN was obtained for the as-grown films with <28% InN. However, for films with higher than 28% InN, the samples showed a spinodally decomposed microstructure as confirmed by TEM and extra spots in SAD patterns that corresponded to multiphase InGaN.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={El-Masry, NA and Piner, EL and Liu, SX and Bedair, SM}, year={1998}, month={Jan}, pages={40–42} }
 @article{piner_behbehani_elmasry_mcintosh_roberts_boutros_bedair_1997, title={Effect of hydrogen on the indium incorporation in InGaN epitaxial films}, volume={70}, ISSN={["0003-6951"]}, DOI={10.1063/1.118181}, abstractNote={The InN percent in metalorganic chemical vapor deposition (MOCVD) and atomic layer epitaxy (ALE) grown InGaN was found to be significantly influenced by the amount of hydrogen flowing into the reactor. The temperature ranges for this study are 710–780 °C for MOCVD, and 650–700 °C for ALE. For a given set of growth conditions, an increase of up to 25% InN in InGaN, as determined by x-ray diffraction, can be achieved by reducing the hydrogen flow from 100 to 0 sccm. Additionally, the hydrogen produced from the decomposition of ammonia does not seem to change the InN percent in the films, indicating that the ammonia decomposition rate is less than 0.1%. The phenomenon of having hydrogen control the indium incorporation was not reported in the growth of any other III–V compound previously studied.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Piner, EL and Behbehani, MK and ElMasry, NA and McIntosh, FG and Roberts, JC and Boutros, KS and Bedair, SM}, year={1997}, month={Jan}, pages={461–463} }
 @article{mcintosh_piner_roberts_behbehani_aumer_elmasry_bedair_1997, title={Epitaxial deposition of GaInN and InN using the rotating susceptor ALE system}, volume={112}, ISSN={["0169-4332"]}, DOI={10.1016/S0169-4332(96)00992-0}, abstractNote={The growth of GaInN ternary alloys has been investigated using atomic layer epitaxy. Single crystal films have been deposited at 100 Torr in the 600°C to 700°C temperature range using the rotating susceptor approach. The InN percentage in the deposited films were found to depend on more than just the gas phase In/Ga ratio. In addition to the relative indium to gallium composition of the precursor gases, the indium incorporation was also found to depend on the absolute partial pressures of the reactant gases. The indium incorporation increases with decreasing growth temperatures, and may reach a temperature dependent saturation limit for a given set of growth conditions. Optimization of the ALE growth process has resulted in single crystal films exhibiting band edge room temperature photoluminescence for InN percentages of up to 27% in the GaInN ternary films. In addition, single crystal indium nitride has been grown using the ALE technique at 480°C.}, journal={APPLIED SURFACE SCIENCE}, author={McIntosh, FG and Piner, EL and Roberts, JC and Behbehani, MK and Aumer, ME and ElMasry, NA and Bedair, SM}, year={1997}, month={Mar}, pages={98–101} }
 @article{bedair_mcintosh_roberts_piner_boutros_elmasry_1997, title={Growth and characterization of In-based nitride compounds}, volume={178}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(97)00069-9}, abstractNote={Development of In-based nitride compounds is lagging behind the corresponding Al- and Ga-based compounds. Potential problems facing the growth of Inx Ga1 − x N films and their double heterostructures will be outlined. A tentative model which describes the reaction pathways taking place during the growth of these In-based nitride compounds is presented and is used to explain both our ALE and MOCVD results. In addition, growth parameters leading to the achievement of high values of x, reduction of In metal incorporation and improvement of both the structural and optical properties of InGaN, AlGaInN and InN will be discussed. Properties of AlGaN/InGaN/AlGaN and AlGaInN/InGaN/AlGaInN double heterostructures will be presented, with emission wavelengths in the 400–550 nm range.}, number={1-2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Bedair, SM and McIntosh, FG and Roberts, JC and Piner, EL and Boutros, KS and ElMasry, NA}, year={1997}, month={Jun}, pages={32–44} }
 @article{piner_behbehani_elmasry_roberts_mcintosh_bedair_1997, title={Impurity dependence on hydrogen and ammonia flow rates in InGaN bulk films}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.119775}, abstractNote={H, C, and O impurity concentrations in metalorganic chemical vapor deposition grown InGaN were found to be dependent on the hydrogen and NH3 flow rates. By increasing the hydrogen flow rate from 0 to 100 sccm, a decrease of greater than two orders of magnitude in the C and O impurity levels and one order of magnitude in the H impurity level was observed. Increasing the NH3 flow rate from 1 to 5 slm results in a decrease in the C concentration and an increase in the H and O concentrations indicating that high purity NH3 (99.999%) can be a significant source of O contamination. Additional studies show that when the InN percent in the InGaN films increases, the impurity concentrations increase regardless of changes in the growth conditions. The InGaN films were grown from 710 to 780 °C and the impurity concentrations were characterized by secondary ion mass spectrometry.}, number={14}, journal={APPLIED PHYSICS LETTERS}, author={Piner, EL and Behbehani, MK and ElMasry, NA and Roberts, JC and McIntosh, FG and Bedair, SM}, year={1997}, month={Oct}, pages={2023–2025} }
 @article{joshkin_roberts_mcintosh_bedair_piner_behbehani_1997, title={Optical memory effect in GaN epitaxial films}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.120414}, abstractNote={We report on memory effects in the optical properties of GaN and AlN epitaxial-films grown by atmospheric pressure metal organic chemical vapor deposition. After exposing selected areas of particular samples with He–Cd laser light (3.8 eV), we observed a persistent and marked decrease in the near band edge photoluminescence (PL) intensity emitted from these areas. This effect has been observed in epitaxial films that typically have a pyramidlike hillock surface. This ability to modulate PL emission intensity at individual points in these materials can be exploited as a method for optical data storage. A means of erasing information stored using this effect has also been investigated using lower energy (∼2 eV).}, number={2}, journal={APPLIED PHYSICS LETTERS}, author={Joshkin, VA and Roberts, JC and McIntosh, FG and Bedair, SM and Piner, EL and Behbehani, MK}, year={1997}, month={Jul}, pages={234–236} }
 @article{zeng_smith_lin_jiang_roberts_piner_mcintosh_1997, title={Optical transitions in InGaN/AlGaN single quantum wells}, volume={15}, number={4}, journal={Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures}, author={Zeng, K. C. and Smith, M. and Lin, J. Y. and Jiang, H. X. and Roberts, John C. and Piner, E. L. and McIntosh, F. G.}, year={1997}, pages={1139–1143} }
 @misc{mcintosh_bedair_el-masry_roberts_1997, title={Stacked quantum well aluminum indium gallium nitride light emitting diodes}, volume={5,684,309}, number={1997 Nov. 4}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={McIntosh, F. G. and Bedair, S. M. and El-Masry, N. A. and Roberts, J. C.}, year={1997}, month={Nov} }
 @article{elmasry_hussien_fahmy_karam_bedair_1992, title={CRITERION FOR SUPPRESSING WAFER BOW IN HETEROSTRUCTURES BY SELECTIVE EPITAXY}, volume={14}, ISSN={["0167-577X"]}, DOI={10.1016/0167-577x(92)90105-s}, abstractNote={Abstract One problem heteroepitaxial growth faces is the mismatch of thermal expansion coefficients. This mismatch causes bowing in the wafer during cooling down after the growth, which interferes with device fabrication especially the photolithographic processes. Selective epitaxy is found to be effective in eliminating wafer bow and it was experimentally achieved. In this work we develop a model based on basic principles of elasticity theory to predict the bow and to establish a criterion to eliminate this bow by selective epitaxy. It is found that the model is in agreement with our published experimental results in the case of selective epitaxy of GaAs on Si.}, number={1}, journal={MATERIALS LETTERS}, author={ELMASRY, NA and HUSSIEN, SA and FAHMY, AA and KARAM, NH and BEDAIR, SM}, year={1992}, month={Jun}, pages={58–62} }
 @article{hussien_fahmy_elmasry_bedair_1990, title={A CRITERION FOR THE SUPPRESSION OF PLASTIC-DEFORMATION IN LASER-ASSISTED CHEMICAL VAPOR-DEPOSITION OF GAAS}, volume={67}, ISSN={["0021-8979"]}, DOI={10.1063/1.345033}, abstractNote={Laser-induced chemical vapor deposition (LCVD) of GaAs allows deposited film to trace the path of the laser beam, thus making it attractive for several applications. However the localized thermal expansion resulting from the laser-induced temperature rise has to be elastically accomodated in order to prevent lattice defects in the LCVD film. We report on the growth conditions that can be allowed without the occurrence of plastic deformation in the epitaxial films. A model is presented to explain the thermal expansion induced distortion during the deposition process and is compared with experimental results.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={HUSSIEN, SA and FAHMY, AA and ELMASRY, NA and BEDAIR, SM}, year={1990}, month={Apr}, pages={3853–3857} }
 @misc{reeber_chu_bedair, title={Gradient lens fabrication}, volume={4,956,000}, number={1990 Sep. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Reeber, R. R. and Chu, W. K. and Bedair, S. M.} }
 @article{bedair, title={Indium-based nitride compounds}, volume={50}, number={1998}, journal={Semiconductors and Semimetals}, author={Bedair, S. M.}, pages={127–166} }
 @inproceedings{emara_berkman_zavada_el-masry_bedair, title={Strain relaxation in InxGa1-xN/GaN quantum well structures}, volume={8}, number={7-8}, booktitle={Physica status solidi c: current topics in solid state physics, vol 8, no 7-8}, author={Emara, A. M. and Berkman, E. A. and Zavada, J. and El-Masry, N. A. and Bedair, S. M.} }
 @misc{elmasry_bedair_reed_stadelmaier, title={Transition metal doped ferromagnetic III-V nitride material films and methods of fabricating the same}, volume={6,955,858}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={ElMasry, N. A. and Bedair, S. M. and Reed, M. L. and Stadelmaier, H.} }