4H-SiC p-i-n Ultraviolet Avalanche Photodiodes Obtained by Al Implantation

In this letter, we report the first demonstration of a 4H-SiC p-i-n ultraviolet (UV) avalanche photodiode (APD) with its p-layer formed by Al implantation. In order to alleviate the electric field crowding around mesa edge, an appropriately doped p sub-layer with high lateral resistance is added beneath the top p + contact layer, which are both formed by Al implantation into a lightly doped n-SiC layer. The room temperature (RT) dark current of the APD remains lower than 0.1 pA when reverse bias is $\sim 260$ V. A maximum avalanche gain larger than $10^{3}$ can be achieved, while the related breakdown voltage exhibits a positive temperature coefficient of $\sim 25$ mV/°C. The activation energy of dark current as well as the relationship between the dark current and the device active area is studied, which suggests that bulk leakage assisted by residual implantation-induced deep-level defects is the dominant source of dark current at high bias. The RT maximum quantum efficiency of the APD under 0 V bias is 44.4% at 270 nm with a UV/visible rejection ratio larger than $10^{4}$ .