CdTe semiconductor radiation detectors, including CdZnTe detectors, have disadvantages in that they are very difficult to use to measure the γ-ray energy in the high energy region above 1 MeV because of the small mobility of charge carriers, although they can be used at room temperature. It was suggested that a stacked structure of CdTe elements be used in order to improve the sensitivity in the high energy regions. In this paper, it is suggested that a highly precise detector response simulation within 5% errors of the full energy peak efficiency be conducted to provide ideas for the design of the detector structure. The fundamental characteristics of both the CdTe detector and CdZnTe detector were investigated to evaluate the feasibility of the high energy region sensitive Cd_1-xZn_xTe detector.