Photoelectric properties of isotype and anisotype Si/GaN:O heterojunctions

Results of a comprehensive study of electrical and photoelectric properties of isotype (p-Si/p-GaN:O) and anisotype n-Si/p-GaN:O) heterojunctions are reported. The structures were fabricated by chemical vapor deposition of thin films of GaN:O solid solutions on silicon substrates by pyrolytic decomposition of gallium monoammine chloride in the presence of water vapor. Total and spectral photosensitivity and photoresponse kinetics in the current mode under forward and reverse biases, current-voltage characteristics, and saturation open-circuit photovoltage were studied. It was found that in both kinds of heterojunctions the charge distribution near the contacts is mainly governed by carrier capture into interface states (with density estimated to be ∼1014–1015 cm−2) with the formation of depletion layers on both sides of the interface. Photosensitivity mechanisms are analyzed for anisotype and isotype heterojunctions. It is shown that the differential nature of the photoresponse kinetics is related to the recharging of interface states, and the strong rise in the photoresponse signal of a biased anisotype heterojunction is attributed to the phototransistor effect. The proposed energy band models of the heterojunctions consistently describe the observed effects.