Electron-selective contacts for c-Ge(p) substrates by annealing phosphorous-doped PECVD silicon films

In this work we report on an electron-selective contact scheme for p-type c-Ge substrates within the framework of epitaxial-free thermophotovoltaic devices. The technique consists of depositing phosphorous-doped silicon layers by PECVD, which undergo an annealing process at temperatures in the 700°C range. In particular, we compare the suitability of the approach for nanocrystalline and amorphous silicon films, obtaining sheet resistances below 100 Ω/sq. and hole saturation current densities lower than 10µA/cm². By ToF-SIMS analysis we are able to confirm silicon and phosphorous diffusion inside the c-Ge bulk. Finished devices are tested under 1-sun illumination, yielding efficiencies of 4.53% and 6.29% for the amorphous and nanocrystalline-based layers, respectively.