The characteristics of CdTe and CdZnTe semiconductor detectors that can be opearted at the room temperature have been evaluated. The energy resolution of each detector is much superior to that of scintillators though a little inferior to that of Ge(Li), Si(Li) or pure Ge detectors. From a practical point of view those detectors are promising and a few applications are described. The only fault at present is that they are insensitive to rather high-energy g rays. Several efforts to improve the sensitivity of them at high energy region are reported.

  The recent development of the growth of semi-insulating CdTe single crystals by the Traveling Heater Method is reviewed. Both quality and uniformity of the detectors fabricated from the crystals currently grown by the THM will encourage the practical applications of CdTe radiation detectors.

  Recent progress in the growth of Cd_1-xZn_xTe (CZT) using the High Pressure Bridgman (HPB) method has enhanced the potential for greater use of this II-VI compound semiconductor in a wide range of ambient or near ambient temperature, X- and gamma-ray detection applications. This paper describes advances in CZT blank fabrication, electrical contact deposition, detector mounting and device design which have led to improvements in energy resolution at higher photon energies. Also, studies have indicated that the performance of the material at low (<150 keV) energies can be significantly improved by cooling the detector into the sub-zero Centigrade temperature range. Further, we will show how the use of various analytical techniques allows material characteristics to be evaluated prior to detector fabrication, which facilitates in-process quality control and reduced rejections during manufacture. Finally, several areas of potential interest for the future will be discussed.

  A multi-layered structure of CdTe elements has been proposed in order to improve the sensitivity in the high energy regions. The response of a semiconductor detector whose charge carriers mobility is as small as CdTe could be simulated and the degree of sensitivity improvement in the high energy regions could be predicted. Both the experimental result and the simulated result indicates that the full energy peak efficiency in the high energy regions can become high and the energy spectra can be improved by means of the multi-layered structure of detector elements.

  The radiation response of a neutron-irradiated CdTe detector was examined in order to clarify the influence of neutron-induced defects on carrier transport property. Neutron irradiation was performed for a CdTe crystal with the dose from 1.3x10⁹ to 1.6x10¹⁰n/cm². A pulse height and its risetime were simultaneously measured event by event for ¹³⁷Cs gamma source in order to evaluate detector performance. Two-dimensional analysis indicated that the pulse height having fast risetime remarkably decreased with neutron fluence. The electron mobility gradually decreased with neutron irradiation, on the other hand, hole transport property was almost unchanged. The experimental results indicated that the electron trapping center was introduced by neutron irradiation and it gave influence on the detector property.

  A multichannel CdTe radiation detector characterized by simultaneous operation in each channel and individual counting of the number of incident radioactive particles has been developed. Uniformity and stability at the regions of high dose rate are realized by heating the detector to suppress local polarization. The detector is constructed as a 256-channel detector module on a ceramic board with four 64-channel CdTe detector chips and plural IC chips for signal processing. Detector modules assembled in a line are available to various applications. In this paper, construction and characteristics of the multichannel CdTe radiation detector are summarized, and applications to a medical radiography and a detecting system for Compton scattering experiments using synchrotron radiation are also presented.