Title:  Advances in Design Optimization and Growth Technology for High-efficiency Indium Gallium Nitride Photovoltaics

Committee:

Dr. Doolittle , Advisor

Dr. Albert Frazier, ECE

Dr. Shyh-Chiang Shen, ECE

Dr. Ajeet Rohatgi, ECE

Dr. Phillip First, Physics

Abstract: 

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 (MBE) 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.  These advances in material growth and device fabrication are implemented to demonstrate functioning InGaN/GaN double-heterojunction solar cells.  The performance of the devices is inherently limited by the heterostructures as evidenced by simulation and experimental results.  These restrictions can be eliminated by employing InGaN homojunction devices that are currently challenging to fabricate due to the need for thick, high-quality InGaN layers.  To address this issue, a hybrid MBE growth technique is presented.  Finally, the fabrication and integration of InGaN quantum dots for intermediate-band solar-cell applications is investigated. 

            These advances in the understanding of III-nitride solar cells lay the foundations for future high-efficiency InGaN photovoltaics.