Characterization of the Transport Properties of Halogen-Doped CdTe Used for Gamma-Ray Detectors

The mobilities, trapping times, activation energies, and trap concentration have been measured for both holes and electrons in Br and Cl-doped CdTe using the time-of-flight technique. Two electron traps 25 and 50 meV below the conduction band and two hole traps 140 and 350 meV above the valence band have been found. The 10 times larger concentration of levels found in the Br-doped CdTe can be explained using a model that describes the association of cadmium vacancies and substitutional halogens. The physical interpretation of the μι+ product when two levels are present is discussed for this case where the mobility is reduced and the lifetime is increased by trapping-detrapping phenomena. The measurements demonstrate that the material has excellent potential for γ-ray detectors that do not polarize with the proper surface preparation and make good detectors (6 keV FWHM for 122 keV γ-ray).