Long-wavelength LO-phonon generation during hot-electron cooling in polar semiconductors

In a hot-electron system in polar semiconductors a new mechanism is studied theoretically for long-wavelength LO-phonon generation, based on the fusion of hot acoustic phonons. The anharmonic mechanism of the LO-phonon decay into pairs of acoustic phonons is considered together with the reverse process of the fusion of acoustic phonons into the LO ones. Corresponding kinetic equations for the electronic temperature and for the distribution functions of both kinds of phonons are solved numerically in GaAs and CdSe. The relation of the numerical results on the long-wavelength LO-phonon generation, to the recent experiments by Tsen et al. in ultrathin GaAs/AlAs multiple quantum wells is discussed.