Cadmium sulfide passivation of InGaAs/InP mesa p-i-n photodiodes

A cadmium sulfide (CdS) passivation process was demonstrated for the first time on InGaAs/InP p-i-n mesa photodetectors. The passivated devices produced lower reverse bias leakage currents in comparison to devices that received only a thermally deposited SiO₂ film. The subsequent deposition of SiO₂ on the passivated devices produced virtually no change to the aforementioned leakage currents even after undergoing a 3-h, 300°C thermal treatment. In contrast, similar SiO₂ capped devices, fabricated without the CdS passivating layer, show a large increase in leakage current when subjected to the same thermal cycle. Leakage current versus mesa diameter measurements suggest these results are due to reduce surface recombination at the exposed mesa sidewall. X-ray photoelectron spectroscopy (XPS) results indicate the S:Cd ratio of these films to be 0.77.