A Method to Reduce Small-Angle Scattering in Monte Carlo Device Analysis

Ionized-impurity scattering is an anisotropic process showing a high preference for small scattering angles. In a Monte Carlo simulation of a semiconductor device many small-angle scattering events have to be processed, although the contribution of these events to carrier momentum relaxation is small. A new method is presented which reduces the amount of smallangle scattering very effectively. In the simulation an isotropic process is used which yields the same momentum relaxation time as the anisotropic process. A theoretical analysis based on the Boltzmann equation is carried out. Monte Carlo calculations are performed over a wide range of doping concentrations, lattice temperatures and electric fields. No systematic difference is found in the results from the anisotropic and the isotropic scattering models. For a given accuracy, the reduction of needed scattering events and free flights can be more than one order of magnitude at low and medium doping concentrations.