Research on the Growth Condition of CdTe Single Crystal for γ-Ray Detector

CdTe single crystals were grown by the Bridgman method from Te excess solution with a molar ratio of Cd/Te=3/7 and halogens were added to the solution for compensating acceptor center due to cadmium vacancies(VCd). Photoluminescence(PL) and electrical resistivity of the crystals grown under various conditions were measured for examining the incorporation of halogens and its compensation state. It was found that the halogen was incorporated in order from fluorine(F) to iodine(I). Halogen donors(D) incorporated under a growth rate of 6 mm/day and a temperature gradient (ΔT/ΔX) of 20 K/cm form preferentially acceptor complex center(VCd??D) and this leads the crystal to p-type conductivity with unsatisfactory compensation. On the contrary, the donors incorporated under the growth rate of 72 mm/day (or steep temperature gradient) made the crystal s into n-type high resistivity with enough compensation. Good ??-ray response was obtained only for the crystals with enough compensation. Therefore, relatively rapid growth or the growth under steep temperature gradient is required for realizing CdTe γ-ray detector.