AlN Thin-Film Vacuum Ultraviolet Photodetector With High Operating Temperature and High Rejection Ratio

AlN thin-film vacuum ultraviolet (VUV) photodetector was prepared by molecular beam epitaxy (MBE) device on c -Al $_{\text{2}}$ O $_{\text{3}}$ substrate. By a complete surface nitridation of sapphire substrate in nitrogen plasma, the epitaxial preparation of high-quality thin AlN film was realized without any buffer layer. The AlN photodetector has an ultralow dark current ( $\sim$ 40 fA at 20 V), a high VUV/ultraviolet-c (UVC) ( $\textit{R}_{\text{185}}$ / $\textit{R}_{\text{222}}$ ) rejection ratio ( $>$ 10 $^{\text{3}}$ ), a high responsivity (30 mA/W), and an ultrafast response (90%–10% decay time $\sim$ 900 ns) at room temperature. More interestingly, an excellent temperature tolerance of the device can be observed, and there is no obvious degradation in the VUV/UVC rejection ratio and response speed with increasing the temperature from 25 $^{\circ}$ C to 500 $^{\circ}$ C. Even at 500 $^{\circ}$ C, the dark current of the device is only 218 pA at 20 V, and the responsivity can reach to 67.3 mA/W. These results indicate that the device has excellent wavelength selective detection ability and high-temperature detection ability in the VUV band, which can be attributed to the relatively high-quality AlN thin film and the avoidance of the impact of buffer layer. Our findings provide an effective way to realize high-performance AlN VUV photodetector, which can be operated in high-temperature environment.