Radiation Detection with Vertical Gradient Freeze Grown CdZnTeSe Crystals

In this study, we report the growth of detector grade Cd
0.9
Zn
0.1
Te
0.97
Se
0.03
(CZTS) single crystals by a vertical gradient freeze (VGF) method. CZTS is a recently discovered quaternary semiconductor for high-resolution room temperature radiation detection. VGF is a comparatively low-temperature crystal growth method and avoids relative motion between the heater and the ampoule containing the precursor materials that helps minimize thermal drifts or temperature fluctuations. Planar detectors fabricated by deposition of gold contacts on a $4.0 \mathrm{mm}{ }^{\prime} 4.0 \mathrm{mm}{ }^{\prime} 1.7 \mathrm{mm}$ VGF-grown CZTS single crystal demonstrated high bulk resistivity $\sim 10^{10} \Omega-\mathrm{cm}$ and consequently a very low leakage current density of $2.8 \times 10^{-8} \mathrm{A} / \mathrm{cm}^{2}$ at a bias of 100 V. The detectors showed excellent radiation detection performance with 100% charge collection efficiency at 200 V when exposed to Am-241 5486 keV alpha particles. The electron mobility-lifetime $(\mu \tau)$ product was measured to be $3 \times 10^{-3} \mathrm{cm}^{2} / \mathrm{V}$ using a single polarity Hecht analysis which is at par with the recently reported values measured in CZTS grown by travelling heater method (THM). The electron mobility has been calculated to be $964 \mathrm{cm}^{2} \mathrm{V}^{-1} \mathrm{s}^{-1}$ using a time-of-flight (TOF) method, a substantial improvement over that obtained from conventionally grown CZTS single crystals. Using a biparametric digital correction method, the detectors showed a robust peak corresponding to the 662 keV gamma photons when illuminated with a ${ }^{137} \mathrm{Cs}$ radioisotope source.