A Monte Carlo study of multiplication and noise in HgCdTe avalanche photodiodes

A Monte Carlo model is developed for understanding the multiplication process in HgCdTe infrared avalanche photodiodes (APD). A good agreement is achieved between simulations and experimental measurements of gain and excess noise factor on midwave infrared electron injected Hg0.7Cd0.3Te APD manufactured at CEA/LETI. In both cases, an exponential gain and a low excess noise factor - close to unity out to gains greater than 1000 - were observed on 5.1-mu m cut-off devices at 77K. These properties are indicative of a single ionizing carrier multiplication process that is to say in our case the electron. Simulations also predict that holes do not achieve enough energy to impact ionize and to contribute to the gain, which confirms the previous observation. A comparison study is presented to explain the effect of different combinations of scattering processes on the avalanche phenomenon in HgCdTe. We find that alloy scattering with random scattering angle increases multiplication gain and reduces excess noise factor compared to the case including impact ionization only. It also appears that, in the more complete scattering environment, optical phonon scattering delays significantly the onset of avalanche.