CdZnTe Schottky diodes for radiation spectroscopy

Based on raw CdZnTe material provided by eV Products, a division of II-VI Inc., we have established a programme of device fabrication and characterisation. Schottky barrier type devices were fabricated on low grade, 5×5×5 mm³, CdZnTe (CZT) crystals for radiation spectrometers. Ohmic contacts were applied by alloying indium metal onto CZT surfaces. Vacuum evaporated gold metal provided the rectifying contact. All diodes showed good rectification. Schottky barrier heights were calculated using IN measurements and barrier heights were determined to be 0.99 eV for air cleaved and 1.04 eV for methanol/bromine etched surfaces. Photoresponse measurements revealed bulk band gap value around E_g=1.51 eV corresponding to a Zn molar percentage of 6.3% in the CZT. Free carrier concentration was measured using C-V measurements on Schottky diodes and found to vary between mid 10¹¹-10¹² cm^-3 in the bulk CZT. Radiation spectra were collected with Schottky diodes, at 100 V bias, using an Am-241 source. Schottky diodes prepared on low grade CZT material showed reasonable detector performance with photo peak resolution of 19% and a charge collection efficiency of 31%. Comparison is drawn between Au-CZT-Au and Au-CZT-In devices. It is found that the operation of these detectors is sensitive to chemical surface preparation of the raw CZT material prior to contact application, and to exposed surface passivation