Dependence of the electrical properties of stabilized a-Se on the preparation conditions and the development of a double layer X-ray detector structure

Stabilized a-Se films deposited at sufficiently low substrate temperatures are n-like in which electrons can drift but holes are deeply trapped. Such layers can be conveniently incorporated in a multilayer a-Se detector structure to block the injection of holes from the positive electrode. We have shown that a simple double-layer detector structure based on a cold deposited n-layer (which is then annealed) on which an i-like layer is grown can have dark current densities lower than 10−10 A cm−2 at a field of 10 V/μm. The dark current depends on the thickness of the n-like layer. An a-Se X-ray detector for slot scanning was fabricated by having the i-n a-Se photoconductor structure coated onto a CCD chip. The latter detector was shown to have excellent resolution with a modulation transfer function remaining above 0.5 up to a spatial frequency of 11-14 lp mm−1.