Electron and proton irradiation effect on the minority carrier lifetime in SiC passivated p-doped Ge wafers for space photovoltaics

Abstract

We report on the effect of electron and proton irradiation on effective minority carrier lifetimes (${\tau}_{eff}$) in p-type Ge wafers. Minority carrier lifetimes are assessed using the microwave-detected photoconductance decay (${\mu}$W-PCD) method. We examine the dependence of ${\tau}_{eff}$ on the p-type doping level and on electron and proton radiation fluences at 1 MeV. The measured ${\tau}_{eff}$ before and after irradiation are used to estimate the minority carriers diffusion lengths, which is an important parameter for solar cell operation. We observe ${\tau}_{eff}$ ranging from 50 to 230 ${\mu}$s for Ge doping levels between 1E17 and 1E16 at.cm$^{-3}$, corresponding to diffusion lengths of 500-1400 ${\mu}$m. A separation of ${\tau}_{eff}$ in Ge bulk lifetime and surface recombination velocity is conducted by irradiating Ge lifetime samples of different thicknesses. The possible radiation-induced defects are discussed on the basis of literature.