Performance of Cd0.9Zn0.1Te based high-energy gamma detectors in various single polarity sensing device geometries

Detector grade Cd_0.9Zn_0.1Te single crystals were grown using a tellurium solvent method. Crystal blocks of dimensions ~11×11×10 mm³ were prepared for characterization and detector fabrication. The crystals were characterized using optical techniques. Infra-red transmission images revealed a low Te inclusion/precipitation concentration. Pockel´s effect measurements showed fairly uniform depth-wise distribution of the electric field. Detectors in various configurations viz., small pixel, virtual Frisch grid, and coplanar grid were fabricated on the same crystal in turns, and characterized by electrical measurements, alpha spectroscopy, and high energy gamma ray spectroscopy. Current-voltage measurements exhibited very low leakage current of ~5 nA at 1000 V and resistivities of the order of 8.5×10¹⁰ Ω.cm. Electron drift mobilities of the order of 840 cm²/V.s and electron mobility-lifetime products of the order of 2.7×10^-3 cm²/V were calculated using alpha spectroscopy. All the detectors exhibited a distinct peak for the 662 keV gamma rays from a ¹³⁷Cs source. Among all other configurations, the virtual Frisch grid configuration revealed the best resolution of 4.3% (FWHM) for the 662 keV gamma rays.