Study of Gain Spatial Nonuniformity in n-on-p and p-on-n 4H-SiC Avalanche Photodiodes

In this work, the gain spatial nonuniformity within the active regions of n-on-p and p-on-n 4H-SiC avalanche photodiodes are investigated by using both two-dimensional photocurrent mapping and hot carrier luminescence imaging techniques. Under high gain operation condition, it is found that local photocurrent within the mesa region is always higher in [ $\overline {11}20$ ] direction for the n-on-p device, while the photocurrent is higher in [ $11\overline 20$ ] direction for the p-on-n device. Nevertheless, the hot carrier luminescence emission images show opposite trends. To explain these phenomena, a physical model based on asymmetric carrier accumulation and junction field screening is proposed, which are caused by lateral carrier drift in off-axis-grown epitaxial device structure. The influence of this physical mechanism on the performance of single photon detection is also studied.