Optimization of a guard ring structure in Geiger-mode avalanche photodiodes fabricated at National NanoFab Center

Abstract

A typical Geiger-mode avalanche photodiode (G-APD) contains a guard ring that protects the structure from having an edge breakdown due to the lowering of electric fields at junction curvatures. In this contribution, G-APDs with a virtual guard ring (vGR) merged with n-type diffused guard ring (nGR) in various sizes were studied to find the optimal design for G-APDs fabricated at National NanoFab Center (NNFC). The sensors were fabricated via a customized CMOS process with a micro-cell size of 65 x 65 mu m(2) on a 200mm p-type epitaxial layer wafer. I-V characteristic curves for proposed structures were measured on a wafer-level with an auto probing system and plotted together to compare their performance. A vGR width of 1.5 mu m and a nGR width of 1.5 mu m with an overlapping between vGR and nGR of 1.5 mu m showed the lowest leakage current before the breakdown voltage while suppressing the edge breakdown. Furthermore, the current level of the lowest-leakage-current structure was as low as that of only vGR with a width of 2.0 mu m, indicating that the structure is also area efficient. Based on these results, the design with vGR, nGR, and OL with width of 1.5 mu m is determined to be the optimal structure for G-APDs fabricated at NNFC.