Determination of the excess noise of avalanche photodiodes integrated in 0.35-μm CMOS technologies

The excess noise of avalanche photodiodes (APDs) integrated in a high-voltage (HV) CMOS process and in a pin-photodiode CMOS process, both with 0.35-mu m structure sizes, is described. A precise excess noise measurement technique is applied using a laser source, a spectrum analyzer, a voltage source, a current meter, a cheap transimpedance amplifier, and a personal computer with a MATLAB program. In addition, usage for on-wafer measurements is demonstrated. The measurement technique is verified with a low excess noise APD as a reference device with known ratio k = 0.01 of the impact ionization coefficients. The k-factor of an APD developed in HV CMOS is determined more accurately than known before. In addition, it is shown that the excess noise of the pin-photodiode CMOS APD depends on the optical power for avalanche gains above 35 and that modulation doping can suppress this power dependence. Modulation doping, however, increases the excess noise. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)