A double-barrier heterostructure generator of terahertz phonons: many-body effects

In this paper we study the generation of coherent terahertz phonons in a double-barrier heterostructure (DBH) under the influence of an external applied bias. The system is characterized by an energy difference between the two lowest levels in the well, which resonates with the optical phonon energy, producing a high rate of emission of longitudinal optical (LO) phonons. The strong electron-phonon interaction in a polar semiconductor leads to the formation of a polaron that is relevant close to this resonance. Therefore the levels corresponding to the first excited state and the satellite of the ground state anticross in two polaronic branches. The LO phonon has a very short lifetime. It decays by stimulated emission of a pair of phonons (LO → \widetilde{LO}) + TA) (where TA stands for transverse acoustic). As a consequence an intense beam of TA coherent phonons is produced, which could have several important applications. A rough model of this system has already been presented (Makler S S, Vasilevskiy M I, Weberszpil J, Anda E V, Tuyarot D E and Pastawski H M 1998 J. Phys.: Condens. Matter 10 5905). Several improvements to that model are presented here. Besides the more accurate treatment of the electron-phonon interaction, the phonon-phonon interaction is considered here taking into account the fact that the whole system is out of equilibrium. The results confirm that the proposed phonon laser is reliable.