Band structure anisotropy effects on the ultrafast electron transport in 4H-SiC

We study band structure anisotropy effects on the electron transport transient in 4H-SiC subjected to electric fields parallel and perpendicular to the c-axis direction. Coupled Boltzmann-like energy-momentum balance transport equations are solved numerically within a single equivalent isotropic valley picture in the momentum and energy relaxation time approximation. The electron drift velocity is shown to be higher in the direction parallel to the c-axis than that perpendicular to it, due to the electron effective mass being larger in the former direction. The ultrafast transport regime develops on a subpicosecond scale (≲0.2 ps) in both directions, during which an overshoot in the electron drift velocity is observed at 300 K for sufficiently high enough electric fields (> 60 kV/cm).