Anisotropic high-field diffusion of holes in silicon

Abstract

Anisotropy of the silicon valence band leads to a strong dependence of charge carrier transport properties, upon the orientation of the electric field. A detailed anisotropic Monte Carlo method has been applied to the calculation of the hole diffusion coefficient in silicon, studying its dependence on field magnitude and orientation. The longitudinal diffusion coefficient is found to have a dependence on the field orientation which is similar in degree to the more familiar dependence of the drift velocity on field orientation. However, it is found that the transverse diffusion coefficient has a substantially stronger dependence on field orientation. At the highest field which has been studied, 50 kV/cm, the transverse diffusion coefficient almost doubles as one shifts from a field oriented in the [100] direction to one in the [101] direction and considers the [101̄] transverse direction.