  The aim of this work is to describe the behavior of a device capable to
generate high frequency (~THz) acoustic phonons. This device consists in a
GaAs-AlGaAs double barrier heterostructure that, when an external bias is
applied, produces a high rate of longitudinal optical LO phonons. These LO
phonons are confined and they decay by stimulated emission of a pair of
secondary longitudinal optical (LO_2) and transversal acoustic (TA) phonons.
The last ones form an intense beam of coherent acoustic phonons. To study this
effect, we start from a tight binding Hamiltonian that take into account the
electron-phonon (e-ph) and phonon-phonon (ph-ph) interactions. We calculate the
electronic current through the double barrier and we obtain a set of five
coupled kinetic equations that describes the electron and phonon populations.
The results obtained here confirm the behavior of the terahertz phonon laser,
estimated by rougher treatments.
