Dark current analysis in high-speed germanium p-i-n waveguide photodetectors

We present a dark current analysis in waveguide-coupled germanium vertical p-i-n photodetectors. In the analysis, a surface leakage current and a bulk leakage current were separated, and their activation energies were extracted. The surface leakage current originating from the minority carrier generation on the Ge layer sidewalls, governed by the Shockley-Read-Hall process and enhanced by the trap-assisted-tunneling process, was identified as the main contribution to the dark current of vertical p-i-n photodiodes at room temperature. The behavior of this surface leakage current as a function of temperature and reverse bias voltage is well reproduced by using the Hurckx model for trap-assisted-tunneling.