GAUGE-INVARIANT FORMULATION OF THE INTRACOLLISIONAL FIELD-EFFECT INCLUDING COLLISIONAL BROADENING

A gauge-invariant formalism is presented for describing nonperturbatively the effects of the electric field on electron-phonon scattering in a nondegenerate semiconductor. The Kadanoff-Baym nonequilibrium formulation of many-body systems is employed to treat the intracollisional field effect and collisional broadening on equal footing. We derive an analytic, gauge-invariant model for the spectral density function and for the density of energy states that accounts for both effects simultaneously in a relatively simple and rigorous way.