Generation of high-frequency coherent acoustic phonons in a weakly coupledsuperlattice

In this work we analyze conditions of generation of high frequency coherent acoustic phonons in a biased semiconductor superlattice. We show that the electron perpendicular transport provides the electron population inversion for interwell phonon-assisted transitions and generation of phonons propag ating along the superlattice axis. The generation rate is large and exceeds the phonon losses in perfect superlattices. Under such conditions, the pho non subsystem is unstable with respect to generation of the coherent phonon modes. Influence of the phonon spectra modification in the superlattice on the generation rate is examined. Effects restricting the intensity of the phonon generation are also pointed out. (C) 1999 American Institute of Phys ics. [S0003-6951(99)00323-X].