First CMOS Silicon Avalanche Photodetectors With Over 10-GHz Bandwidth

This letter reports on the first silicon avalanche photodetectors (APDs) with over 10-GHz bandwidth. Three types of APDs based on P+/N-well junction are realized in standard complementary metal-oxide-semiconductor (CMOS) technology. For bandwidth improvement, the CMOS-compatible APDs (CMOS-APDs) are designed to be smaller active area, and a spatially-modulated avalanche photodetector (SM-APD) is also proposed in order to further reduce the bandwidth limiting factor of the CMOS-APDs. Current-voltage characteristics, responsivities, and photodetection frequency responses of the three APDs are measured and compared, and the photodetection bandwidth characteristics are analyzed with an equivalent circuit model to identify the origin of the bandwidth improvement. The proposed small-area CMOS-APD provides 10-GHz bandwidth with high responsivity, and the SM-APD achieves 12-GHz bandwidth, which is the largest bandwidth ever reported for silicon photodetectors in standard CMOS technology.