@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 (Jpk) above 1000 A/cm2 with minimal absorption losses due to the use of thin (<50 Â) GaAs layer. We will report on the growth and device modeling of these structures as well as the effect of high temperature annealing on Jpk. A method to grow TJ structures resistant to annealing will be described, which has resulted in thermally annealed TJ with Jpk 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 In0.49Ga0.51P 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 A 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 pi-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$_x$ Ga$_{1-x}$As $_{1-z}$P$_z$ /Ga$_{1-y}$In $_y$P (x > y ) 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 $_x$Ga$_{1-x}$ As$_{1-z}$P $_z$ wells and Ga $_{1-y}$In$_y$ P barriers (x > y) 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} } @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 InxGa1-xAs wells with very thin GaAs0.2P0.8 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} } @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 In0.14Ga0.76As wells balanced with GaAs0.24P0.76 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 In0.17Ga0.83As wells and GaAs0.25P0.75 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, τtn. While this EQE decrease is undesirable in practical devices, it is useful for determining the recombination lifetime, τr, 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, Ptot, was varied until the calculated EQE fit the experimental data. The value of Ptot was then correlated to the only unknown parameter, the recombination lifetime. Using this method the recombination lifetime in In0.17Ga0.83As 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{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{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} } @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{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={Abstract}, 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{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} }