Amplification of optical phonons in bulk semiconductors and heterostrutures at Low temperatures

The amplification of optical phonons both in the bulk semiconductors (the drift of 3D electron gas) and in heterostructures (2D gas) is investigated theoretically. The principal obstacle for observing the amplification of the optical phonons is the heating of the electron gas under drifting. Therefore the low temperatures T <; 77 K are considered, and the electron gas is assumed as degenerated. Both hydrodynamic and kinetic approaches have been applied. The kinetic approach yields more adequate values of the increments of instability.