Charge Trapping Effects in THM- and VGF-Grown CdZnTeSe Radiation Detectors

The performance of the state-of-the-art Cd1-xZnx Te1-ySey (CZTS) detectors, an emerging wide bandgap high-resolution room-temperature semiconductor radiation detector, is currently limited by the presence of various charge trapping centers including impurities and intrinsic point defects. In this article, we compare the performance of two CZTS single crystals grown using two different methods viz., traveling heater method (THM) and vertical gradient freeze (VGF) method. Detectors in a planar configuration have been fabricated from the THM- and VGF-grown crystals. Both types of detectors exhibited very high bulk resistivity $\approx 10^{10}~\Omega $ -cm. The electron mobility-lifetime ( $\mu \tau$ ) product in the THM-grown detector was calculated to be $2.9\times 10^{-3}$ cm2/V—higher by a factor of 4 than that of the VGF-grown crystal detector. On the other hand, the electron drift mobility in the VGF-grown detector was calculated to be twice that of the THM-grown detector. The observed drift mobility of 1245 cm2/V.s in the VGF-grown detector is the highest mobility reported in CZTS. The concentration and capture cross section of the traps, studied using photoinduced current transient spectroscopy (PICTS), have been found to define the contrasting charge transport properties observed in the two CZTS detectors. Biparametric (BP) correlation studies using 662-keV gamma photons revealed that the effect of hole trapping was more prominent in the THM-grown detector.