High Signal-to-Noise Ratio Avalanche Photodiodes With Perimeter Field Gate and Active Readout

This letter describes an avalanche photodiode (APD) fabricated in a 0.5-μm CMOS process. In Geiger mode, the APD had an area-normalized dark count rate as low as 2 Hz/μm2at room temperature. Its signal-to-noise ratio (SNR) increased by an order of magnitude as a result of perimeter field gating. We demonstrate that under high-illumination conditions, perimeter field gating maximizes SNR, whereas under low-light conditions, it maximizes sensitivity.