Photo-Current Multiplication Phenomenon of Amorphous Silicon-Based Multilayer Photodiodes Fabricated on Crystalline Silicon Substrate

Abstract

Recently, high-resolution and high-density solid-state imaging devices have been in high demand due to their high photogain because the smaller pixel size makes the smaller photo-current dependent on the reduced area. Multilayer photodiodes having a-SiC:H/a-Si:H/a-SiN:H structures fabricated on the crystalline silicon (c-Si) substrate were studied for their photo-multiplication effects which marked a gain of 6.6. These multiplication phenomenona arose in the wavelength region longer than 550 nm, while in the shorter-wavelength region, the photogain was less than unity. This is explained by the electron carrier process where the carriers photogenerated in the c-Si substrate are accumulated at the a-SiN:H/c-Si interface and tunneled via localized states in the a-SiN:H layer by the induced high electric field. From these results, it is considerably difficult to support the theory of avalanche effect to explain these photo-multiplication effects.