Leakage Current Behavior in Common I-Layer A-SI:H P-I-N Photodiode Arrays

Hydrogenated amorphous silicon photodiode arrays form the basis of monolithic threedimensional integrated circuit sensor technology. In these arrays, the intrinsic a-Si:H layer covers the entire area to maximize light collection. One technique by which the pixel diode is defined, is to pattern the bottom contact layer independently of the intrinsic layer. One of the most important characteristics of any diode array, however, is that the dark-state reverse bias leakage currents must be as low as possible to minimize diode noise. This study examines the leakage currents associated with the pixelated array. These structures are unique in that the edge of the diode is defined by the local electric field between diodes, rather than the physical surface of an a-Si:H film. The effect of the diode edge has been found to induce a field-dependent component to the reverse bias leakage current. For example, diodes with 5500A i-layer, have a junction leakage of 14 to 20 pA/cm 2 ,a t 5.0 x1 0 4 V/cm, while the pixel edge-dependent current component can be as high as 30 pA/cm 2 . In addition, it will be shown that the i-layer thickness and junction doping plays a key role in determining the behavior of the leakage currents.