Plasma-Wave Instability in Narrow-Gap Semiconductors

In narrow-gap semiconductors, the energy of conduction-electron plasma oscillations can be made equal to the band gap by doping. When such a crystal is pumped with an electron beam or light wave, stimulated emission of plasma waves takes place. Estimates of growth rate suggest that, in ${\mathrm{Pb}}_{1-X}{\mathrm{Sn}}_X\mathrm{Se}$ and ${\mathrm{Pb}}_{1-X}{\mathrm{Sn}}_X\mathrm{Te}$ alloys, collisional losses can be overcome and the plasma waves excited to high amplitude.