Avalanche Gain Modeling Revisited in HgCdTe APDs

The gain in short-wave infrared and mid-wave infrared HgCdTe avalanche photodiodes (APDs) with large diameters has been analyzed using an already established model based on an empirical expression proposed by Okuto–Crowell (OC) and a new model derived for the impact ionization in HgCdTe. This model is based on a simplified but physical description of the carrier dynamics during the multiplication. It is shown that OC model has limitations in giving a precise description of the measured avalanche gains, and that is difficult, in view of present available data, to derive a universal expression for the model parameters to predict the avalanche gain in HgCdTe APDs as a function of the Cd composition, operating temperature, and multiplication layer geometry. The new model is shown to give a better fit of the gain data, associated with a scaling of the model parameters with the band gap.