Mobility of Polarons in Semiconductors

The polaron mobility of a semiconductor is studied on the basis of kinetic equation for polaron subsystem interacting with equilibrium phonon subsystem in the presence of small external electric field. The mobility is discussed with a connection to polaron subsystem velocity relaxation. Relaxation processes in the system are studied on the basis of spectral theory of the collision integral operator in the presence of the electric field. Contribution of the electric field to the velocity relaxation time equation is found in the simplex approximation comparing this equation with the Newton second law. The basic equations of the theory are solved by the method of truncated expansion in the Sonine polynomial series. The velocity relaxation coefficient and mobility of polaron are calculated in one-polynomial approximation. It is established that the nonequilibrium polaron distribution function differs from the Maxwell distribution with polaron velocity and temperature. Relation of the developed theory with the Bogolyubov method of the reduced description of nonequilibrium systems is discussed. For semiconductors of the groups A(III)B(V) velocity relaxation coefficient and mobility are found numerically.