Vertical Gradient Freeze Growth of Detector Grade CdZnTeSe Single Crystals

We report the growth of detector grade Cd0.9Zn0.1Te0.97Se0.(03) (CZTS) single crystals, a recently discovered quaternary semiconductor for room temperature radiation detection, by a vertical gradient freeze (VGF) method. VGF is a comparatively low-temperature growth method and avoids relative motion between the heater and the ampoule containing the precursor materials which minimizes any thermal drift or temperature fluctuations. As a result, CZTS single crystals with superior charge transport properties has been obtained. Growth of detector-grade CZTS single crystals using VGF method has not been reported yet. X-ray spectroscopy based elemental analysis showed that the grown crystals demonstrated the desired stoichiometry required for high resolution radiation detection. Planar detectors fabricated by deposition of gold contacts (similar to 0.07 cm(2)) demonstrated high bulk resistivity similar to 10(10) Omega-cm and a very low leakage current density of 2.8 x 10(-8) A/cm(2) at a bias of 100 V when measured at room temperature. The detectors showed excellent radiation response with 100 % charge collection efficiency when exposed to 5486 keV alpha particles. The electron mobility-lifetime (mu tau) product was measured to be 3 x 10(-3) cm(2)/V using a single polarity Hecht analysis which is at par with the recently reported values measured in CZTS grown using conventional Bridgman or travelling heater method. The electron mobility has been calculated to be 964 cm(2) V(-1 )s(-1) using a time-of-flight (TOF) method, a substantial improvement over that obtained from conventionally grown CZTS single crystals.