High energy resolution CdTe Schottky diode γ-ray detectors

Schottky diode X/γ-ray detectors based on semiinsulating CI-doped CdTe crystals have been developed and investigated. Both the Schottky and Ohmic contacts were formed by vacuum deposition of Ni electrodes on the opposite faces of (111) oriented CdTe crystals pre-treated by Ar ion bombardment with different parameters. Record-low leakage current in the fabricated Ni/CdTe/Ni structure at high voltages (~5 nA at 300 K for the area of 10 mm² at bias voltage of 1500 V) was achieved that was caused by the charge transport mechanisms which were interpreted on the basis of known theoretical models. The developed detectors have shown the record-high energy resolution in the measurements of the spectra of ¹³⁷Cs and ⁵⁷Co isotopes (FWHM of 0.42% and 0.49%, respectively). From a comparison of the spectra taken with the detector irradiated from the Schottky contact side and from the opposite side with an Ohmic contact, the concentration of uncompensated impurities (defects) in the CdTe crystals has been determined. The obtained value has been found to be close to the optimal one.