Current transport mechanisms of InGaN metal-insulator-semiconductor photodetectors

The authors report on InGaN metal-insulator-semiconductor (MIS) photodetectors with two different insulating layers of Si3N4 and Al2O3 deposited via plasma-enhanced chemical vapor deposition and atomic layer deposition, respectively. The photoresponse spectra show that the metal-Al2O3-InGaN photodetector exhibits an approximately threefold higher photoelectric responsivity and a larger spectral rejection ratio as compared to the metal-Si3N4-InGaN photodetector at a 1 V reverse bias. The current transport mechanisms in MIS photodetectors were investigated in order to determine the difference in photoresponse. The results show that the space charge limited current is a dominant leakage conduction mechanism in the InGaN MIS photodetectors, but this mechanism is mediated by the exponential trap distribution in the metal-Si3N4-InGaN photodetector. This indicates a higher density of trap states in the Si3N4 bulk. A bidirectional Fowler–Nordheim tunneling effect was observed in the metal-Si3N4-InGaN photodetector, which indicates high trap states in the Si3N4 bulk and the Si3N4–InGaN interface. These traps increase the probability of photogenerated carrier recombination in the bulk of the dielectrics and at the interface of dielectric-InGaN, and hence the photoelectric responsivity is lower.