Single Photon Counting Spatial Uniformity of 4H-SiC APD Characterized by SNOM-Based Mapping System

In this letter, a mapping system based on a scanning near field optical microscope is built to characterize the single photon counting spatial uniformity of single photon avalanche photodiodes (SPAD), which is important for device physics study and process optimization. The system comprises of a passive quenching circuit module and a mapping module, which are used to record single photon count (SPC) signals and to scan over the SPAD photo-sensitive area, respectively. Meanwhile, 4H-SiC UV SPADs with positive beveled mesa are designed and fabricated. For the first time, 2-D mapping of SPC uniformity of 4H-SiC SPADs is carried out at different over-bias voltages. The possible reasons for the observed SPC non-uniformity across the active area of the 4H-SiC SPAD are discussed.