We investigated theoretically the compositional dependences of deep-level ionization energies, and its possible influence on compensation, and photosensitivity in large bandgap semiconductors. Experimentally, it was illustrated in a semi-insulating Cd1-xZnxTe ingot grown by the vertical Bridgman method, whose properties can be explained by the increase in the C-band extrema on an absolute energy scale with an increase of the Zn content, and by the nature of a deep-donor level that is contingent upon the host-crystal's defect states. (C) 2009 Elsevier B.V. All rights reserved.