Effect of CdTe crystal thickness on the efficiency of Cr/CdTe/Au Schottky-diode detectors

The effect of CdTe crystal thickness on the detection efficiency and energy resolution of Cr/CdTe/Au diode X/γ-ray detectors has been studied. The Schottky (Cr electrode) and near Ohmic (Au electrode) contacts were created using Ar plasma treatment of the B- and A-faces of CdTe(111) single crystals at different regimes, respectively. Detector-grade CdTe wafers with an area of 5 × 5 mm2 and thicknesses d of 0.5 mm, 0.75 mm, 1.0 mm and 2.0 mm were used. High energy resolution (FWHM) in the 137Cs spectra (662 keV peak) was achieved: from 0.5 % for thin detectors to 3.0 % for thick ones. From the comparison of the detection efficiency dependences on the CdTe crystal thickness with the corresponding calculated dependences, the uncompensated impurity concentration in CdTe was obtained as N ≈ 4 × 1010 cm−3. N determines the space–charge region width W in Schottky diodes, therefore the effect of this value on the detection efficiency was analyzed. A key feature of the efficiency calculation was the correct evaluation of the electric field strength in the crystals and also using the integration limit d rather than W when W > d (in contrast to the earlier works).