Gigahertz photodetectors fabricated in heteroepitaxial Ge-on-Si for use in integrated receivers

Heteroepitaxy of a low band gap semiconductor can enable 1.3-1.55 μm photodetectors on Si integrated circuits. We fabricated ion implanted interdigitated P-I-N photodetectors in low energy plasma enhanced chemical vapor deposited Ge-on-Si with a graded buffer. The Ge layer had 1.5x10^5 cm^-2 threading dislocation density, 3.3 nm rms surface roughness, and bulk-like optical properties. Measurements at 1.3 μm wavelength gave 49 % quantum efficiency and, at -3V bias, 4.6 nA/μm^2 dark current density, and 3.5 GHz bandwidth. Numerical simulations calculated pair generation and carrier transport in a unit cell. Detector behavior was predicted by a combination of unit cell equivalent circuit models. Modeling predicted modifications to achieve 10 Gbps bandwidth.