Optical-Power Dependence of Gain, Noise, and Bandwidth Characteristics for 850-nm CMOS Silicon Avalanche Photodetectors

We investigate the effects of incident optical powers on the performance of 850-nm silicon avalanche photodetectors (APDs) realized with P
⁺
/N-well junctions in standard CMOS technology. The current-voltage characteristics, responsivities, avalanche gains, noise power spectral densities, excess noise factors, electrical reflection coefficients, and photodetection frequency responses of the fabricated CMOS-APD are measured for different incident optical powers. In addition, the photodetection frequency responses at different incident optical powers are modeled with equivalent circuits and the influence of the optical power on photodetection bandwidth is analyzed. From these, we show that, near the avalanche breakdown voltage, the CMOS-APD avalanche gain and excess noise factor increase and photodetection bandwidth decreases with decreasing incident optical power. These results should be very useful for realizing high-performance CMOS integrated optical receivers for various optical-interconnect applications.