Evaluation of 5 mm-thick CdTe detectors from the company Acrorad

Using 2×2×0.5 cm³ cadmium telluride (CdTe) substrates from the company Acrorad, we have fabricated detectors with planar cathode contacts and 8×8 anode pixels. We investigate the I-V characteristics and energy resolution of the detectors for different contact materials and surface treatments. After biasing the detectors for a certain time, the dark currents increase dramatically. Our studies show that the time before breakdown decreases for higher detector temperatures and for higher applied bias voltages. We obtained the best results with a Pt cathode contact and In anode pixels when we heat the detector to 90°C for 30 minutes prior to depositing the In contacts. Flood-illuminating the detector with 662 keV X-rays, we measured the pulse length distribution and derived an electron mobility of ∼860 cm² V^-1s^-1. We show that the energy resolution can be improved by correcting the anode signals for the depth of the primary interaction. Operated at a temperature of -40°C and a cathode bias voltage of -500 V, the best pixels of the best detector achieved full width half maximum (FWHM) energy resolutions of 8 keV (6.4%) and 23 keV (3.4%) at 122 keV and 662 keV, respectively.