High field density-functional-theory based Monte Carlo: 4H-SiC impact ionization and velocity saturation

Abstract

We present 4H-SiC electron and hole Monte Carlo transport calculations that are obtained using the density functional theory (DFT) calculated conduction and valence band density-of-states (DOS) curves. The transport properties include room temperature average electron-hole velocities, energies, and impact ionization rates as functions of applied fields, as well as mobilities. This is achieved employing detailed DFT-DOS curves, which obviate the need to consider electron-hole energy dispersion details that are generally calculated using the empirical pseudopotential method. Thus the proposed method facilitates fast computations of carrier-phonon and semiclassical field-carrier interactions, and the relevant field-dependent averages. Specifically, our calculated average electron velocities peak at 1.6×107 cm/s for 0.2 MV/cm field bias, and the simulated electron ionization coefficients match well with experimental data in the 3–5 MV/cm range. To obtain similar averages for 4H-SiC’s holes, we resolve the hole transport semiclassically in conjunction with hole-phonon couplings, but also include additional quantum tunnelinglike effects to determine experiment corroborated ionization rates. Our calculated average hole velocities saturate at roughly 1×107 cm/s after 0.5 MV/cm. Further, the hole ionization coefficients, which are considerably higher than the electron ionization coefficients, match with experimental data for a wide range of field values ≥2 MV/cm.