Optimization of multi-stage avalanche photodiode structure based on InGaAs/InAlAs

Avalanche photodiodes (APD) can amplify the photoelectric signal based on the avalanche multiplication effect of carrier to improve the sensitivity of detection. They have the characteristics of low noise and high gain, so they are suitable for long-distance optical communication. In this work, a multi-stage avalanche photodiode structure with SAGCM (Separated Absorption, Grading, Charge and Multiplication region) is proposed based on Impact Ionization Engineering (I²E). The photocurrent, dark current, electric field, gain and noise characteristics of InGaAs/InAlAs avalanche photodiodes are studied by optimizing the grading layer's thickness and doping concentration. According to the final simulation results, the optimized avalanche photodiodes has low excess noise. At 60 V voltage and 300 K temperature, the noise factor k value (the ratio of impact ionization coefficients) of the five-stage APD is 0.012, and the gain can reach 430.