A method to reduce small-angle scattering in Monte Carlo device analysis

Abstract

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 small-angle 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.