Enhanced Au/semi-insulating single-crystal CdTe Schottky-type radiation detectors based on van der Waals contacts

Cadmium telluride (CdTe) remains a leading semiconductor material for room-temperature high-energy radiation detection. Despite advances in single-crystal growth that have pushed CdTe’s resistivity near its intrinsic limit, detectors still suffer from current noise under high bias. Schottky contacts or p-n junctions are commonly employed to suppress leakage current while preserving charge transport, but their performance in bulk CdTe is hindered by strong Fermi level pinning. We demonstrate a van der Waals (vdW) contact integration approach that mitigates Fermi level pinning and significantly reduces dark current. This study presents a novel approach to enhancing Schottky-type X/γ-ray detectors based on semi-insulating CdTe crystals by employing vdW contacts. Gold (Au) electrodes were mechanically transferred onto CdTe surfaces to minimize surface damage and mitigate Fermi level pinning. Cross-sectional transmission electron microscopy (TEM) confirms the absence of atomic intermixing at the Au-CdTe interface, validating the non-invasive nature of the vdW contact. In contrast, Au contacts deposited by evaporation show residual contamination, as revealed by X-ray photoelectron spectroscopy (XPS), along with increased defect states confirmed by low-temperature photoluminescence (PL). For mechanically-transferred contacts (vdW), both XPS and PL spectra closely match those of pristine CdTe, indicating minimal surface degradation. This improved interface quality correlates with an increase in the Schottky barrier height from 0.78 eV to 0.82 eV. As a result, Au/CdTe/Au detectors with vdW contacts exhibit reduced dark current and improved energy resolution (from 14.4% to 11.8%) for 59.5keV γ-rays from a 241Am isotope. These findings demonstrate the potential of vdW contact engineering to significantly improve the performance of CdTe-based radiation detectors.