Modeling of band-to-band tunneling transitions during drift in Monte Carlotransport simulations

The conventional method of semiconductor charge carrier transport investiga tions using full band ensemble Monte Carlo simulations is extended to allow for tunneling between bands during accelerated drift of the carriers. The essentially classical picture of transport, as simulated, is preserved by i mplementing a stochastic selection of the band index of the initial state o f each scattering process associated with phonons, with impurities, or with impact ionization. Relative probabilities for the band assignment are calc ulated from the overlap integrals of the cell-periodic parts of Bloch wave functions belonging to different bands, for k-vectors along the carrier k-s pace trajectory between successive scattering events. As an example, the me thod is applied to Monte Carlo transport simulations for holes in 4H SiC in a homogeneous applied electric field. Tunneling between valence bands duri ng the drift phases is shown to have a significant impact on the carrier en ergy distributions when large electric fields are applied, and on physical parameters that directly depend on the carrier energy, such as the hole ini tiated impact ionization coefficient. (C) 2000 American Institute of Physic s. [S0021-8979(00)04315-2].