Effects of Buffer Layers on Performance of Amorphous Silicon Image Sensors

Abstract

ABSTRACTThis paper reports the effects of a-SiC:H buffer layers on a-Si:H photodiode properties, especially the dark current and decay image lag. The photodiode has an ITO/p-type a-SiC:H/a-Si:H/i-type a-SiC:H/metal structure.Using two heterojunctions–p-SiC:H/a-Si:H at the surface contact and a-Si:H/i-SiC:H at the back contact–significantly decreases the dark current. The p-SiC:H layer blocks electron injection, and the i-SiC:H layer suppresses the reaction between the a-Si:H layer and metal electrode. The use of both a-SiC:H layers may increase decay image lag. Excess boron doping to the p-SiC:H layer induces boron diffusion into the a-Si:H photo-electric conversion layer, which increases trap levels in the a-Si:H layer. The i-SiC:H layer, because of its high resistivity, decreases the electric field applied to the a-Si:H photo-electric conversion layer. Optimizing the amount of boron in the p-SiC:H layer and the resistance of the i-SiC:H layer enabled us to produce the characteristics required for high-definition television (HDTV) image sensors–a dark current on the order of 10−10 A/cm2 and a 1% level decay image lag.