Optimization of structural and growth parameters of metamorphic InGaAs photovoltaic converters grown by MOCVD

Abstract

Metamorphic Ga0.76In0.24As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In0.24Al0.76As/p-In0.24Ga0.76As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 1018 cm–3 and completely remove the potential barrier, thereby reducing the series resistance of the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.