Application of multiscattering theory to impurity bands in Si:As

Impurity bands in arsenic-doped silicon have been calculated for doping densities of 3.3×1017, 1.2×1018, and 8.0×1018 cm−3. A multiscattering approach is used with a model potential which provides both electronic screening and the proper bound-state energy for the isolated center. The results are in good agreement with previous calculations based on electron hopping among hydrogenic centers. An advantage of the multiscattering approach is that it treats the conduction-band states as well and shows the loss of these states to the formation of the impurity band. This is a new result and affects the density for the Mott transition. Calculations are also performed for the states associated with the binding of an extra electron to unionized arsenic centers, the so-called D− band. The overall results are in good agreement with the observed Mott transition in Si:As near 8×1018 cm−3.