CdTe has been regarded as the most suitable semiconductor for X- and gamma-ray detectors operated without cryogenic cooling. Nevertheless, CdTe manufacturers are confronted by severe difficulties caused mainly by the poor transport properties of the material. Takahashi et al. [1,2] reported a significant improvement of the characteristics of the CdTe detectors based on utilizing a Schottky barrier. However, some crucial questions, relevant to the role of the Schottky diode in this type of detectors, remain unanswered.
In this presentation, we focus on spectral distribution of the Schottky detector efficiency, the most comprehensive characteristic of the device. For the first time, in our calculations we take into consideration both the charge loss in the depletion layer with account for nonuniformity of the electric field, and the collection of charges generated in the neutral region of the diode. The detection efficiency spectrum of the stacked detector [3] is also reported.
The preliminary evaluation indicates that the obtained results are conclusive and important. (i) The total charge collection in the depletion region is achieved for the electron lifetime in excess of about 0.01 microseconds rather than several microseconds as in a detector with ohmic con-tacts. (ii) The "diffusion" component of the collected charge can be comparable and even greater in comparison with the commonly considered "drift" component. (iii) For typical parameters of the material, the efficiency of a stacked detector containing more than 8-10 Schottky diodes can be in excess of the "bulk" detector efficiency.

[1] T. Takahashi et al. Proc. SPIE. 3446 29 (1998).
[2] T. Takahashi et al. Nucl. Instr. and Meth. A436 111 (2000).
[3] S. Watanabe et al. IEEE Trans. Nucl. Sci. 49 1292 (2002).

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