High-resolution CdTe radiation detectors with single-polarity charge sensing technique

Cadmium telluride (CdTe) radiation detectors applied three-electrode and pixel structure have been fabricated from commercially available CdTe crystals (2 mm thick). In case of a three-electrode detector, the cathode was 6×6 mm², the anode was 0.5 mm in diameter and the third electrode surrounding the anode was I mm width. The gap between the third electrode and the anode was 0.25 mm. In case of pixel detectors, the anodes were 9 pixels and the guardring surrounded the pixels. One pixel detector has rectangular 1.35×1.35 mm² pixels with 1.45 mm pitch and the other pixel detector has rectangular 0.7×0.7 mm² pixels with 0.8 mm pitch. All electrodes were formed on the crystals by vacuum evaporation of Au. Pulse height spectra of gamma-rays emitted from a ¹³⁷Cs source were acquired with the fabricated detectors. The three-electrode detectors were operated with the anode voltage of +10 V, the cathode voltage of -540 V and the third electrode grounded. An energy resolution of 6.0 keV FWHM was recorded for 662 keV gamma-rays at room temperature. The pixel detectors with 1.35×1.35 mm² pixels and with 0.7×0.7 mm² pixels have exhibited energy resolutions of 16.7 keV and 12.3 keV FWHM at 662 keV, respectively. The pixel detectors were operated at 600 V and at room temperature. Detailed discussions about the device fabrication, operation and characterization are given in this paper