Spectral analysis of In_XGa_1-xN/GaN quantum well structures for III-nitride based solar cells

This paper reports on the optical and electrical characteristics of III-nitride epi-structures for visible wavelength absorption. Structures, incorporating In_xGa_1-xN/GaN (0.20<x<0.35) quantum well active regions have been analysed by photocurrent spectroscopy, optical transmission and electro/photo-luminescence techniques to identify the key spectral absorption characteristics of the structures. In addition the influence of indium composition and number of quantum wells on the spectral response of such structures was investigated. In order to demonstrate the effect of different indium compositions on the photovoltaic performance of an InGaN solar cell, an active silicon solar cell was stacked under two InGaN structures with differing indium composition. For higher indium composition, a lower spectral response is observed at zero bias and correspondingly lower quantum efficiency by a factor of approximately two. The obtained results provide insight how multi-junction solar cells incorporating III-nitride solar cells might be designed in a multi-junction configuration in order to boost the overall efficiency of conventional cell materials such as silicon.