Monte Carlo simulation of low-noise avalanche photodiodes with heterojunctions

A Monte Carlo model is developed to simulate avalanche photodiodes with AlGaAs/GaAs heterojunctions. The experimentally observed ultralow-noise behavior of a center-well avalanche photodiode is successfully reproduced in the model. It is found that the arrangement of different materials in the intrinsic region can modulate the positional dependence of impact ionization events, and hence the gain distribution. Consequently, the noise is sensitive to the structural parameters such as well thickness. Hot and energetic electrons are distinguished by their distribution in k space. This distinction is used to explain why the noise behavior is sensitive to the initial carrier excess energy from photogeneration but relatively insensitive to carrier energy gained from the electric field.