A numerical study of carrier impact ionization in AlxGa1−xN

Using a full-band Monte Carlo model we have computed the carrier impact ionization coefficients in AlxGa1−xN for seven alloy compositions between x = 0 (GaN) and x = 1.0 (AlN). We have found that holes dominate the impact ionization process for compositions below 50%, while electrons dominate for larger aluminum contents. The model also predicts that, due to the particular features of the AlxGa1−xN valence band structure, holes impact ionization processes are effectively negligible for aluminum composition above 60%. Furthermore, we find that the electron-alloy scattering significantly reduces the electron ionization coefficients leading to the dominant behavior of holes in for an aluminum composition below 50%.