The effects of proton irradiation on the current-voltage and capacitance-voltage characteristics of GeSn/Si photodiodes

Current-voltage and frequency-dependent capacitance-voltage measurements were performed on heterojunction p-Ge1-xSnx/n-Si devices before and after 2-MeV proton irradiation and then after annealing at 120 and 200 degrees C. The Ge1-xSnx/Si devices were fabricated by a novel remote plasma-enhanced chemical vapor deposition process. Sn concentrations in the deposited GeSn layer range from 2.7 to 7.1%. In post-irradiation measurements, donor and carrier concentration remained constant, but the ideality factor increased above two, n > > 2. Series resistance improved by three orders of magnitude, perhaps indicating that the contacts are no longer Ohmic. The donor carrier concentration of silicon is two orders of magnitude larger than GeSn. A significant increase in the forward current density post-irradiation potentially signifies an increase in deep-level trap concentration.