Phonon band population inversion in GaN 
Romuald BRAZIS , Romas RAGUOTIS , Daniel Nausewicz 
Semiconductor Physics Institute, A.Gostauto 11, Vilnius LT2600, Lithuania 
Abstract 
Gallium nitride crystals with their comparatively highenergy phonons, and strong electronphonon coupling, seem to be promising for the phonon band population inversion affecting the twophonondifference absorption of infrared radiation. We devote this work to the theory of phonon generation by electrons in ntype GaN crystals at the lattice temperature T between 300 and 10 K, including deformation and piezopotentials, as well as ionized impurity contributions to the scattering rate of electrons. We determine the nonequilibrium phonon numbers using our calculated Monte Carlo data on phonon generation rate and literature data on phonon lifetimes. We conclude the inelastic process of optic phonon emission by electrons to be dominating in the electric field range from 1 to10 kV/cm, and the optic phonon band population to be much in excess compared to the acoustic one at the same wave vector values. We give a trial of the phononphoton coupling constant values for the twophonondifference process together with the nonequilibrium phonon number values, including photon reabsorption by free carriers, to calculate the resulting absorption coefficient. It turns out to be higly sensitive to electric fields in the range from 1 to 10 kV/cm, in the photon frequency range of 1520 THz.

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Presentation: oral at EMRS Fall Meeting 2003, Symposium A, by Romuald BRAZIS Submitted: 20030509 11:45 Revised: 20090608 12:55 