A Study on a Photoconductive Layer and Pixel Electrodes for an Avalanche-Type Solid State Imager Overlaid with a Photoconductive Layer.

The constitution of a photoconductive layer and pixel electrodes for an avalanche-type solid-state imager overlaid with an a-Se photoconductive layer is studied. To achieve a stable avalanche phenomenon under high electric fields, a blocking structure against charge injection into the photoconductive layer from the electrodes is required. Pixel electrodes with a sufficiently flat surface are also needed to avoid breakdown caused by the local maximums in the electric field To reduce the electric fields in the vicinity of each electrode, we use an As2Se3 layer between the cathode and the a-Se layer, and a LiF-doped a-Se layer between the anode and the a-Se layer. This also reduces the dark current. Flat pixel electrodes are formed by p+-layers in a n-type Si substrate By using these techniques, an avalanche multiplication factor larger than 20 is attained on a MOS type linear image sensor overlaid with an a-Se photoconductive layer.