The relation between deep trapping levels and the structure of Se layers

Abstract

Using electron microscopy methods it has been determined that there are numerous crystalline inclusions in evaporated layers of amorphous selenium. The density, dimensions, modification and distribution in the cross section of a layer are essentially dependent upon the method of layer preparation. The maximum micro-inclusion density is observed in layers evaporated at a substrate temperature ( t s) between 8 to 30°C. These layers also possess crystallites of monoclinic modification. In layers evaporated at t s ⩾ 50°C inclusions of trigonal modification prevail. The parameters of the deep trapping levels for holes and electrons have been determined from photodischarge kinetics. The origin of these levels is found to be related to the phase transition. The hole traps are caused by the crystalline formation of trigonal modification, and the electron traps by crystallites of monoclinic modification.