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

We report on the effect of electron and proton irradiation on effective minority carrier lifetimes ($τ_{eff}$) in p-type Ge wafers. Minority carrier lifetimes are assessed using the microwave-detected photoconductance decay ($μ$W-PCD) method. We examine the dependence of $τ_{eff}$ on the p-type doping level and on electron and proton radiation fluences at 1 MeV. The measured $τ_{eff}$ before and after irradiation are used to estimate the minority carriers diffusion lengths, which is an important parameter for solar cell operation. We observe $τ_{eff}$ ranging from 50 to 230 $μ$s for Ge doping levels between 1E17 and 1E16 at.cm$^{-3}$, corresponding to diffusion lengths of 500-1400 $μ$m. A separation of $τ_{eff}$ 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.