A theory of the transport and recombination properties of photoexcited carriers in germanium and silicon at low temperatures

Abstract

A theoretical study is made of the properties of carriers which are photoexcited into one of the bands of a semiconductor with mean energy in excess of the thermal energy. Carrier heating then occurs if the recombination process is faster than the electron-phonon thermalization process. Detailed numerical calculations are made of the carrier distribution functions in germanium and silicon at low temperatures arising from excitation by room temperature black-body radiation and cascade capture into shallow impurities. The calculations employ acoustic deformation and nonpolar optical scattering and show that heating occurs below 30K for ionized impurity densities of order 10¹⁵ cm^-3. The hot phototransport parameters for acoustic deformation and ionized and neutral impurity scattering are derived by a perturbation analysis and Monte Carlo techniques.