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 solid-state imagers. A new a-Si:H photo-conversion layer, fabricated by the laminar-flow photo-chemical-vapor-deposition method, is overlaid on the vertical CCD scanning circuitry in the sensor. The photodegradation behavior of a-Si:H photodiodes is investigated in terms of dark-current density, electron /spl mu//spl tau/ product and transient photocurrent. These properties are degraded as a result of light-induced defects in the a-Si:H layer. The Staeblar-Wronski constants, C/sub sw/, are estimated to be 7.5/spl times/10/sup -7/ at no voltage and 1.1/spl times/10/sup -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 determined by the degradation of the transient photocurrent, and is estimated to be about 2.2/spl times/10/sup 8/ h for 1 lx light exposure. The lifetime is considered to be improved compared with that of previous-type photodiode reported before (1.5/spl times/10/sup 7/ h for 1.5 lx light exposure) and clearly satisfies the needs for practical use of the device.