Simulation analysis of high-field carrier transport in wide-bandgap semiconductors considering tunable band structures and scattering processes

Abstract

Though the high breakdown electric field of wide-bandgap semiconductors is usually attributed to their large bandgap, the impacts of other band structure parameters and scattering processes on impact ionization phenomena have not been clarified yet. This study computationally analyzes the effects of band structures and scattering rates on the high-field carrier transport properties such as impact ionization coefficients and drift velocity in wide-bandgap semiconductors. For that purpose, this study adopts Monte Carlo simulations in which the E–k dispersion and scattering rates are directly tuned. Simulations with varied band structures indicate that an average of the group velocity in the whole Brillouin zone is a dominant factor determining the impact ionization coefficients rather than the effective mass at the band edge. In addition, the Brillouin zone width has critical impacts when Bloch oscillations occur, which significantly suppress impact ionization. As for scattering mechanisms, the roles of inelastic scattering processes including impact ionization in energy relaxation are discussed. It is also revealed that elastic scattering contributes to energy relaxation processes through transitions of electrons to higher bands. This mechanism leads to the unintuitive positive temperature dependence of impact ionization coefficients when Bloch oscillations occur. These results obtained by the theoretical analyses in this study can serve as basic physical insight to understand the behaviors of impact ionization coefficients in wide-bandgap semiconductors.