Amplification of acoustic phonons in a degenerate semiconductor superlattice

Amplification of acoustic phonons propagating along the axis of a semiconductor superlattice (SL) is investigated using the microscopic theory. A non-quantizing electric field is applied to the SL to produce a drift velocity vD of the charge carriers and whenever vD exceeds vs (sound velocity) amplification occurs. The threshold field E0 at which absorption switches over to amplification depends on the SL parameters and vs. It is noted that E0 in SL is by far lower than that in bulk semiconductors and that there exists the possibility of finding a field E∗ such that −Γ(E∗)⩾Γ(−E∗). This allows, in principle, the use of SL as hypersound generator.