High Detection Efficiency 4H-SiC Avalanche Photodiode With Off-Center Top Electrode Structure

In this work, we report a high single photon detection efficiency 4H-SiC ultraviolet (UV) avalanche photodiode (APD) with an off-center top electrode structure. To alleviate the lateral-carrier-drift induced non-uniform gain distribution of SiC APDs, a half-ring shape top electrode structure is designed, in which the electrode is off-center placed on the$[11\overline 2 0]$side of the circular mesa. Based on 2-dimensional photon count mapping, it is demonstrated that such device design can notably reduce the top electrode shadowing effect on the high-gain light sensitive region, thereby improving the single photon detection efficiency (SPDE) of the SiC APD. When operating in Geiger mode based on an active quenching circuit, the fabricated APD with the off-center top electrode structure shows a high SPDE of 36.7%, which is 28.7% higher than that of the control device with traditional symmetric electrode. Meanwhile, a relatively low dark count rate of ~14.4 Hz/$\mu $m2 is obtained. This work provides a new strategy for designing high detection efficiency SiC APDs.