Semiconductor gamma detector systems, that are not sensitive to hole trapping, are improved by trading off the bulk electrical resistivity and the gamma electrons' lifetime. CdTe and CdZnTe detectors are prepared from donor doped crystals, grown by the low pressure Bridgman method with cadmium vapor pressure control. Donor doping, and annealing in tellurium vapors, adjusts the crystal's electrical resistance to high n-type value. The level of doping optimizes detector operation. Uniform detector arrays with good energy resolution are achieved.