Light-soaking effects on a-Si : H photodiodes deposited by the laminar-flow photo-CVD method

A 2/3-in, 2-Mpixel, STACK-CCD imaging sensor has been developed for HDTV so lid-state imagers. A new a-Si: H photo-conversion layer, fabricated by the laminar-flow photochemical-vapor-deposition method, is overlaid on the vert ical CCD scanning circuitry in the sensor. The photodegradation behavior of a-Si : H photodiodes is investigated in terms of dark-current density, ele ctron mu tau product and transient photocurrent. These properties are degra ded as a result of light-induced defects in the a-Si: H layer. The Staeblar -Wronski constants, C-sw, are estimated to be 7.5 x 10(-7) at no voltage an d 1.1 x 10(-7) at a reverse voltage of 6 V applied to the photodiode during light-soaking with an AM-1 lamp. The lifetime of the photodiode is determi ned by the degradation of the transient photocurrent, and is estimated to b e about 2.2 x 10(8) h for 1 Ix light exposure. The lifetime is considered t o be improved compared with that of previous-type photodiode reported befor e (1.5 x 10(7) h for 1.5 Ix light exposure) and clearly satisfies the needs for practical use of the device.