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. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3622298]