Energy and spin relaxations in drift transport of carriers: effects of polar optical hot phonon generation

We study the energy and spin relaxations in drift transport of electrons in n-doped GaAs. Stating from the rate of change of phonon occupancy in a relaxation time approximation and the electronic power dissipated in a drifted Maxwellian distribution, the hot phonon generation in high field transport and its effect in electronic spin relaxation are investigated. The scattering is confined to polar optical phonon incorporated by implementing the Ehrenreich's variational approach in the scattering process. It is found that a finite phonon lifetime can reduce the energy relaxation rate and hence can increase the momentum relaxation rate, resulting in lowering the mobility or delaying the runaway to higher fields, where the effect increases with electron density. The electron spin is found to relax with a frequency of sub-THz, and the spin lifetime ((s)) is found to decrease with increasing the strength of the drifting field. However, a high field completely depolarizes the electron spin due to an increase of the spin precession frequency of the hot electrons via the longitudinal polar optical phonon scattering. It is also found that (s) increases with increasing the moderately n-doping density up to about 1 x 10(17) cm(-3) or decreasing the crystal temperature. However, a high density decreases it abruptly. The results are discussed on the basis of the Dyakonov-Perel (DP) spin relaxation mechanism.