Investigation on Cd_(0.9)Zn_(0.1)Te_(1-y)Se_y single crystals grown by vertical Bridgman technique for high-energy gamma radiation detectors

摘要

Cd_xZn_(1-x)Te_(1-y)Se_y (CZTS) is an emerging wide bandgap semiconductor material for the applications of high-resolution room-temperature x-ray and gamma-ray detectors. Large volume Cd_(0.9)Zn_(0.1)Te_(1-y)Sey single crystal ingots were grown by vertical Bridgman technique with composition y = 0.02, 0.03, 0.05, and 0.07. Several planar detectors were fabricated on single grain cut out from the grown ingots and characterized. Current-voltage (I-V) measurements revealed very low leakage current (≤ 1 nA) at an operating bias voltage of ≥ 100 V and a bulk resistivity of ～10~(10) Ω-cm. X-ray diffraction (XRD) results showed sharp diffraction peaks, which confirmed a highly crystalline structure of the grown crystals. Energy dispersive x-ray spectroscopy (EDX) showed uniform elemental distribution over a large area and confirmed the stoichiometry of the samples. While all the detectors showed response to alpha particles, the detector with composition y = 0.03 showed very good ~(137)Cs (662 keV) gamma response. The drift mobility and mobility-lifetime product in all the samples of those compositions were calculated for both electrons and holes. Pulse height spectroscopy using ~(137)Cs on the fabricated detectors showed fully resolved 662 keV gamma peaks with an energy resolution of ～2%. A one-to-one correlation between the space charge limited current (SCLC) flow and radiation detection properties was found to exist in these crystals. An anomalous current flow mechanism, falling outside the comprehension of SCLC flow mechanism, has been observed in the rest of the samples. The anomalous behavior has been attributed to the presence of electron traps.