The calculated results of voltage responsivity and specific detectivity versus doping level of semiconductor is represented for uncooled PEM detector on the basis of MCT single crystals with composition of x = 0.2. The optimal level of an acceptor doping of material is defined. The design as well as main photoelectrical parameters PEM detector for middle range of IR-range of spectrum (3-7 mum) is also shown. (C) 2004 Elsevier Ltd. All rights reserved.