Reduction of the dark current in stabilized a-Se based X-ray detectors

Abstract

The carrier ranges in vacuum deposited stabilized amorphous selenium films have been studied as a function of substrate temperature during deposition. While the electron range remains relatively unaffected, the hole range drops sharply with decreasing substrate temperature. At low substrate temperatures, the hole range becomes sufficiently shorter than the electron range, which means that such layers can replace the alkali doped hole trapping layers in the multilayer amorphous selenium based X-ray detector structures. We have produced double layer amorphous selenium based detector structures using the same starting material but varying the fabrication processes through the following steps: deposition of a thin cold hole trapping layer, a so called n-layer; annealing of the n-layer; and a much thicker layer that can transport both holes and electrons is grown at an elevated substrate temperature on the annealed n-layer. The structures produced by this technique have dark current densities that are similar to the ones reported for the presently commercialized amorphous selenium p–i–n-like structures (⩽10−10Acm−2 at 10Vμm−1).