Asymmetric surface modification of CdTe single crystals for electrode optimization in photon-counting detectors

CdTe is an outstanding photon-counting detector material, especially for next-generation medical diagnostic CT. However, CdTe detectors still face critical challenges under high bias voltages, such as polarization effects and high leakage current. This paper aims to address these issues through electrode optimization. Initially, the crystals were characterized to select those suitable for detector fabrication. The high crystalline quality was confirmed by X-ray diffraction (XRD), and the impurity content was analyzed using inductively coupled plasma mass spectrometry (ICP-MS). And the optical properties were systematically evaluated via ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopy and infrared transmittance measurements. Subsequently, four samples taken from the top part of the ingot were selected, and their cathode and anode surfaces were etched with a bromine-methanol solution. After which the anode side was subjected to KOH etching for varying durations. Among them, the wafer etched for 30 s was used to fabricate detector CT-2. Under non-irradiation conditions, CT-2 exhibited a forward current of 1.34 mA at +100 V, which is 2.4 times the value of the detector that was not subjected to wafer etching. Additionally, the corresponding reverse leakage current at − 100 V was reduced from 71 nA to 20 nA. Under irradiation conditions, the photocurrent increased linearly with X-ray irradiation doses during both the on and off stages, exhibiting excellent repeatability without response degradation or obvious polarization. The α-particle energy spectra of CT-2 were acquired under different bias voltages, revealing an optimal energy resolution of 13.74% at 160 V. From these spectral data, the mobility-lifetime product was derived using the single-electron model fit, giving a value of 2.16 × 10⁻³ cm²/V. These results demonstrated the effectiveness of asymmetric surface modification in optimizing electrodes and enhancing the overall performance of CdTe single-crystal detectors.