Effects of thermal cycle annealing on reduction of defect density in lattice-mismatched InGaAs solar cells

Abstract

Lattice-mismatched In 0.16Ga 0.84As solar cells were grown on GaAs substrates using graded In x Ga 1− x As buffer layers and homogenous In 0.16Ga 0.84As buffer layers. The indium composition x in the graded buffer changed from 0% to 16% continuously. Thermal cycle annealing (TCA) was performed after the growth of the graded buffer layers. The effects of TCA on the solar cell open-circuit voltage and quantum efficiency have been investigated. The minority carrier lifetime is observed to increase in the p-type In 0.16Ga 0.84As layer after applying the TCA process. Electron-beam-induced current microscopy also shows a related reduction in dislocation density in the p-type In 0.16Ga 0.84As layer after TCA processing. Cross-sectional transmission electron microscopy performed on the graded buffer layer suggests that the strain present in the cell layers is reduced after the TCA process, implying that the TCA treatment promotes strain relaxation in the graded buffer layers.