Nonlinear transport in n-III-nitrides: Selective amplification and emission of coherent LO phonons

The nonequilibrium macrostate of the lo phonon system in strongly-polar n-doped III-nitrides, in the presence of electric fields of intermediate to high intensities, is characterized. The emergence of a kind of resonance consisting in the selective amplification of lo vibrations in a privileged and localized off-centre region of the Brillouin zone is demonstrated. It has an associated phenomenon akin to a Cherenkov-like effect involving a preferential emission of lo phonons in a selected cone with its axis along the direction of the electric field. Moreover, it has predicted the onset of emission (stimulated amplification) of weakly decaying coherent lo phonons generated by the drifting electrons.