Cadmium telluride (CdTe), which has a high average atomic number and a unique band structure, is a leading material for room-temperature \(\textrm{X}\) / \(\gamma\) -ray detectors. Resistivity and mobility are the two most important properties of detector-grade CdTe single crystals. However, despite decades of research, the fabrication of high-resistivity and high-mobility CdTe single crystals faces persistent challenges, primarily because the stoichiometric composition cannot be well controlled owing to the high volatility of Cd under high-temperature conditions. This volatility introduces Te inclusions and cadmium vacancies ( \({\text {V}_{\text {Cd}}}\) ) into the as-grown CdTe ingot, which significantly degrades the device performance. In this study, we successfully obtained detector-grade CdTe single crystals by simultaneously employing a Cd reservoir and chlorine (Cl) dopants via a vertical gradient freeze (VGF) method. By installing a Cd reservoir, we can maintain the Cd pressure under the crystal growth conditions, thereby preventing the accumulation of Te in the CdTe ingot. Additionally, the existence of the Cl dopant helps improve the CdTe resistivity by minimizing \({\text {V}_{\text {Cd}}}\) density through the formation of an acceptor complex ( \(\hbox {Cl}_{\text {Te}}\) - \(\hbox {V}_{\text {Cd}}\) ) \(^{-1}\) . The crystalline quality of the obtained CdTe(Cl) was evidenced by a reduction in large Te inclusions, high optical transmission (60%), and a sharp absorption edge (1.456 eV). The presence of substitutional Cl dopants, known as \(\hbox {Cl}_{\text {Te}}^+\) , simultaneously supports the record high resistivity of \({1.5 \times {10}^{10}}\,{\Omega }\,{\cdot }\,\hbox {cm}\) and remarkable electron mobility of 1075 ± \({88}\,\hbox {cm}^{2}\,\hbox {V}^{-1}\,\hbox {s}^{-1}\) simultaneously, has been confirmed by photoluminescence spectroscopy. Moreover, using our crystals, we fabricated a planar detector with \(\mu \tau _\text{e}\) of \({(1.11 \pm 0.04) \times 10^{-4} \, \text {cm}^2/\text {V}}\) , which performed with a decent radiation-detection feature. This study demonstrates that the vapor-pressure-controlled VGF method is a viable technical route for fabricating detector-grade CdTe crystals.
