Amorphous silicon carbide rear-side passivation and reflector layer stacks for multi-junction space solar cells based on germanium substrates

New developments for space solar cells mainly address efficiency improvements and weight reduction. In this paper we developed amorphous SiC based layer stacks for passivation and enhanced reflection on thin and lowly doped (2×1016 − 1×1017 at/cm3) Ge wafers. Passivated Ge samples with minority carrier lifetimes of more than $300\ \mu \mathrm{s}$ and surface recombination velocities of just 17 cm/s are presented. Thermal annealing at 400°C and additional “mirror” layer deposition do not harm the minority carrier lifetimes or lead to an even slight increase. Electron irradiation with fluences of 1×1015 e/cm2and more lead to strong material degradation and lifetimes of just $5\ \mu \mathrm{s}$.