Advances in Design Optimization and Growth Technology for High-Efficiency Indium Gallium Nitride Photovoltaics
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Indium gallium nitride (InGaN) alloys, are a promising candidate for high-efficiency solar applications because of their highly-attractive inherent properties and the widely-available manufacturing infrastructure for the growth and fabrication of nitride-based devices. However, the full potential of InGaN for photovoltaic applications requires significant progress in the areas of device design, material growth, and device fabrication. The goal of this work is to evaluate the viability of InGaN alloys for high-efficiency solar cell applications. Numerical simulations are employed to provide guidelines for the design of high-efficiency InGaN-based solar cells and to identify present and future material limitations. The growth of InGaN alloys over the entire composition range by molecular beam epitaxy is then investigated with the goal of eliminating phase separation and improving the crystal and optical quality. The electrical and structural properties of doped III-nitride films, required to create the collecting p-n junction, are studied. Several fabrication aspects that are necessary for the fabrication of InGaN-based solar cells, are developed. The improved material quality and the developed fabrication process are implemented to demonstrate functioning InGaN/GaN double-heterojunction solar cells. These advances in the understanding of III-nitride solar cells lay the foundations for future high-efficiency InGaN photovoltaics.