Dipole scattering from ion pairs in compensated semiconductors

The electron scattering cross sections for both a screened and an unscreened ion pair dipole have been calculated. They are smaller than the corresponding cross sections for a single charge by a factor of about (2πL/λ)2 where L is the dipole length (~ 10−8 cm) and λ the electron wavelength (~ 10−6 cm). The electron mobility for scattering by dipoles is approximately proportional to T12N−1dm−32 for a nondegenerate carrier distribution and n13N−1dm−2 for one that is degenerate, (n = electron density, Nd = dipole density, T = temperature, m = effective mass). In a highly compensated semiconductor dipole scattering can give an appreciable contribution to the mobility. Numerical values are given for germanium having highly mobile lithium as the compensating donor impurity. For example, dipoles account for a quarter of the electron scattering at 100°K for donor and acceptor concentrations of about 1019 cm−3, differing by one per cent.