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 (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 approximate to 50 to 230 mu s for Ge doping levels between 1 x 10(17) and 1 x 10(16) at.cm(-3), corresponding to diffusion lengths of approximate to 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.