Capture Process by Shallow Donors in Silicon at Low Temperatures

Abstract
Thermal capture by shallow attractive impurities has been studied by the Monte Carlo method at low temperatures. In order to model this process, the perturbation produced by the highest excited impurity states associated to the ideal Coulombic potential and the multiphonon mechanism were combined in the same simulation procedure. These excited states are considered to produce an energy quasicontinuum or impurity band where the carrier can move assisted by lattice phonons. To characterize the ground-state capture, the transition rates of multiphonon transitions from the impurity band and from the conduction band have been included. Electron capture cross sections have been calculated as a function of the temperature and compared with experimental data from the P⁺, As⁺ and Sb⁺ shallow donors in Si, achieving a good fitting with the Huang-Rhys factor, S, as the only free parameter.