Magnetophonon Structure in the Longitudinal Magnetoresistance of Nonpolar Semiconductors

The magnetophonon effect in nonpolar nondegenerate semiconductors is investigated by solving the Boltzmann equation exactly in the Ohmic limit for combined optical- and acousticphonon scattering of carriers in parallel electric and magnetic fields. The solution is used in computing the longitudinal magnetoresistance at several temperatures and ratios of acousticto optical-phonon scattering. As this ratio increases from zero at intermediate temperatures, the Gurevich-Firsov (GF) resonance maxima are found to broaden and shift toward higher magnetic field, with pronounced minima developing at the resonance fields before the magnetophonon structure vanishes at large acoustic-phonon scattering. As the temperature increases, additional (pseudoresonance) minima develop between the GF extrema, and are comparable in amplitude to the latter when kT approximates the optical-phonon energy. At these temperatures the GF extrema are minima, even in the absence of elastic scattering. The results are compared with displaced-Maxwellian computations. The various effects are explained by physical arguments, which suggest that the same effects should occur for polar materials also.