Influence of Nucleation Layers on MOVPE Grown GaAs on Ge Wafers for Concentrator Solar Cells

A novel process for the nucleation layer of GaAs on p-Ge wafers using MOVPE has been developed. It is based on a low temperature process with two steps: 1) a predeposition of a monolayer of Ga or As and 2) the subsequent of a GaAs buffer layer at low temperature. In this paper, a study of the characteristics of n-on-p GaAs solar cells grown on Ge wafers as a function of these nucleation conditions has been performed. In addition, SIMS and C-V-measurements have been used to analyze the diffusion processes taking place across the GaAs/Ge interface. From all of these measurements it can be concluded that a low temperature nucleation layer reduces the Ge out-diffusion. In addition, the predeposition of a Ga monolayer decreases the As diffusion into the Ge wafer as well as the Ge diffusion into the GaAs layer and results in improved solar cell characteristics (higher quantum efficiencies and fill factors) as compared to the predeposition of an As monolayer