Laser emission from PbSe and ${\mathrm{Pb}}_{1-x}{\mathrm{Sn}}_x\mathrm{Se}$ diodes has been investigated under hydrostatic pressure of up to 15 kbar near liquid-nitrogen temperature. The dominant modes, as well as their spacing and their slope and the threshold current necessary to get laser action, have been studied under pressure, and by varying the carrier concentration of the diode substrates. We have observed the laser effect on both sides of the band crossing on a single diode and we show that the laser effect is limited in energy to the value of the mixed plasmon-phonon oscillator. To interpret these experiments quantitatively, we have developed a model for the laser action. In this model, we use the calculated dielectric constant of an inverted medium in the case of nonparabolic bands. We have also been led to evaluate quantitatively the density of states tail as well as the spontaneous- and stimulated-emission rates in these salts. The agreement between theory and experiment is good before the band crossing point, but after it, discrepancies appear that we discuss in detail.

• Received 23 February 1973

DOI:https://doi.org/10.1103/PhysRevB.8.4693