Microcrystalline germanium thin films prepared by the reactive RF sputtering method

We focus on thin film microcrystalline germanium (μc-Ge) as narrow gap semiconductor materials for high infrared sensitivity and consider applying it to thermo-photo-voltaic (TPV). The μc-Ge films were prepared on glass substrates by the reactive RF sputtering method with Ar and H₂ gas mixtures. We could successfully produce photosensitive μc-Ge films. Higher crystallinity structures do not always result in better carrier properties. Probably, the amorphous portions between crystalline grains have important roles to suppress the grain boundary defects. We applied the μc-Ge to i-layers of pin structure devices, and observed the photovoltaic effect for the first time.