Cd-related inclusion heterogeneity in Cd-rich nominally undoped CdTe single crystals for radiation detection

Cadmium telluride (CdTe) is an important room-temperature semiconductor for X/γ-ray detection, for which high resistivity and uniform electrical properties are required. In nominally undoped CdTe, however, the high-resistivity state is highly sensitive to stoichiometry and native-defect compensation. In this work, Cd-rich nominally undoped CdTe single crystals were grown by the vertical Bridgman method, and the relationship between electrical nonuniformity, Cd-related bulk defects, and radiation response was investigated. Multi-position current-voltage measurements revealed resistivities ranging from 1.1 × 10 6 to 7.8 × 10 9 Ω cm within a wafer. Infrared microscopy revealed sparse inclusions measuring 3.6–6.3 μm in the high-resistivity specimen and denser inclusion clusters measuring 24.4–27.5 μm in the low-resistivity specimen. Both specimens exhibited X-ray rocking-curve full widths at half maximum of approximately 0.03° and infrared transmittances of approximately 64%, suggesting that the electrical difference was mainly associated with the heterogeneous bulk-defect distribution. Te-atmosphere annealing modified the defect morphology and increased the resistivity from 3.5 × 10 6 to 9.9 × 10 6 Ω cm, although residual inclusions remained. Au/CdTe/Au devices fabricated from the high-resistivity region showed a linear X-ray response and a measurable 241 Am γ-ray photopeak with an energy resolution of 12.57% at 59.5 keV and 200 V. These results reveal the influence of Cd-related inclusions in nominally undoped CdTe and provide guidance for improving crystal quality.