@article{hagar_routh_abdelhamid_colter_muth_bedair_2024, title={GaN-based tunnel junction with negative differential resistance by metalorganic chemical vapor deposition}, volume={125}, ISSN={["1077-3118"]}, DOI={10.1063/5.0208759}, abstractNote={We present metalorganic chemical vapor deposition-grown III-nitride tunnel junction (TJ) devices showing negative differential resistance (NDR) under forward bias with a peak to valley ratio of 1.3 at room temperature. Previously, NDR in GaN material systems has only been achievable utilizing molecular beam epitaxy or polarization enhanced AlGaN interlayers. The TJ devices presented here utilize structures based on p+InGaN/n+InGaN materials with the n-side of the junction doped with both Si and Mg and with electron and hole concentrations roughly in the 1019 cm−3 range. The Mg precursor flow is maintained at a constant rate during the whole TJ growth. This co-doped technique can eliminate several Mg-related issues such as delayed incorporation, the memory effect, and Mg solid-state diffusion. Structures grown on relaxed InGaN semibulk templates show enhanced hole concentrations and improved TJ performance.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Hagar, B. G. and Routh, E. L. and Abdelhamid, M. and Colter, P. C. and Muth, J. and Bedair, S. M.}, year={2024}, month={Aug} }
 @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 InyGa1−yN 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_bonner_el-masry_bedair_2022, title={Reduction of V-pit density and depth in InGaN semibulk templates and improved LED performance with insertion of high temperature semibulk layers}, volume={5}, url={https://doi.org/10.1088/1361-6641/ac6d01}, DOI={10.1088/1361-6641/ac6d01}, abstractNote={Abstract
               Highly relaxed InGaN templates with an effective In-content of ∼10% that exhibit reduced V-pit density and an improved surface roughness are reported using the semibulk (SB) growth approach. This was achieved by the insertion of five period high temperature SB (HTSB) InGaN SB regions. This report demonstrates that better quality InGaN templates can be achieved by the insertion of HTSB within the templates, rather than by ending the templates with a superlattice structure or by refilling the pits with GaN interlayers. Three SB samples were grown with and without the HTSB layers. Using secondary-ion mass spectrometry, photoluminescence, and x-ray diffraction, the effective In-content of the templates was determined to be 9.6%, 5.8%, and 8.7%. Using atomic force microscopy, the surface roughness was found to improve from 4.4 to 1.7 nm by using the two HTSB regions, and the average V-pit density and depth improved from 7.6 × 10−7 to 4.5 × 10−7 cm−2 and 8.2 to 2.8 nm, respectively. Also, the maximum V-pit depth was reduced from about 30.5 nm to about 9.6 nm in the sample with the HTSB regions. Two LEDs were studied, one with both HTSB regions, and one with only the topmost HTSB. The optical power density of the LED with both HTSB regions was 1.4 times higher at the peak injection current, displayed a ∼1.3 times higher external quantum efficiency peak, and a delay of the EQE droop onset. These results show that higher In-content SB templates can be improved with the implementation of a modified growth approach.}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Routh, E L and Abdelhamid, M and Colter, P C and Bonner, A J and El-Masry, N A and Bedair, S M}, year={2022}, month={Jul} }
 @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
                  Ga1-y
                  N templates on In
                     x
                  Ga1-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
                  Ga1-y
                  N templates with y ∼ 10% can cause a red shift in MQWs emission of 
                     
                     
                        
                           
                              Δ
                           
                        
                        E
                        ∼
                        0.33
                        
                           
                              eV
                           
                        
                     
                     
                  . 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
                  Ga1-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{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} }