Sound amplification by stimulated emission of radiation 0.3 eV. For the same scheme, the usage of a semiconductor heterostructure (layers of different semiconductors) with narrow gap indirect in momentum space between valence and conduction bands may be more effective. This could be more promising since the spatial separation of the layers provides a possibility of tuning the interband transition into resonance by an external electric field. An essential statement here is that this proposed phonon laser can operate only if the temperature is much lower than the energy gap in the semiconductor. During the analysis of this theoretical scheme several assumptions were introduced for simplicity reasons. The
Sound amplification by stimulated emission of radiation dispersion law away from the radiation zone. The importance of this, lies on the fact that electric and in-plane magnetic fields normal to coupled quantum wells, can control the dispersion of indirect exciton. Normal electric field is needed for tuning the transition: direct exciton --> indirect exciton + phonon into resonance and its magnitude can form a linear function with the magnitude of in-plane magnetic field. We note that the mathematical analysis of this scheme considers of longitudinal acoustic (LA) phonons instead of transverse acoustic (TA) phonons. This aims to more simple numerical estimations. Generally, the preference in transverse acoustic