In a single-layer organic photoreceptor, depletion charging and surface charge injection are important issues in the electrophotographic process. During the initial stages of the charging process, a finite amount of free and shallow trap generated charges are swept out of the bulk of the photoconductive layer. Also, surface charges from corona ions can be injected into the layer due to the adsorption of corona generated chemicals on the free surface. Such depletion charging and surface charge injection reduce the charge acceptance. In single-layer high gamma photoreceptors, the charge acceptance is not reduced in any degree in spite of abundant depletable carriers and excess surface charge injection. The photoinduced and dark discharge characteristics of such high gamma photoreceptors are found to be well described by a mathematical structural trap model which takes into account both carrier depletion and surface charge injection.