A simple Monte Carlo (MC) model is proposed to study the avalanche
characteristics of heterojunction avalanche photodiode (HAPD). This model is
capable to simulate the avalanche multiplication and excess noise factor in
HAPDs by including the dead-space effect, hole to electron ionization ratio
and heterointerface probability. The dead-space effect showed a vital role
in reducing noise in single junction HAPDs based on the statistical
determination in our model. It is shown that the dead-space effect reduces
the avalanche noise in heterojunction device due to the localized ionization
events. We found that the dead-space effect and the number of hole feedback
impact ionizations are still the dominant effects to improve the excess
noise factor especially in the injection layer of the device. In addition,
the probability of electron and hole to cross the heterointerface will
eliminate the secondary impact ionizations in the device.