Longitudinal optical-like phonon resonant mid-infrared emission (LORE) and absorption peaks of micro-surface line and space structures of metallic material plates on GaN wafers are observed at 500 – 630 K. The emission peak energy is located in a range of 670 – 730 cm-1 for GaN, which is lower than the LO-phonon energy of approximately 730 cm-1 at 630 K. This feature is contrasted with that of the LO-phonon resonant emission from the Au-GaAs microstructures resonating with the LO phonon. The emission mechanism is clarified using a structure of n++-GaN with an electron density of 1×1020 cm-3 as a metallic material. These emission lines have another notable feature, i.e., the observed peak energies are independent of the polar emission angle, unlike the emissions by surface phonon polaritons showing a significant directive nature of peak energies. The present results show that each peak energy in the emission spectrum is positioned at the zero-point of the real part of the dielectric function comprising the components of the transverse optical phonon and other electric dipoles induced by the LO-like modes, excluding the target mode. This type of emission is also obtained for the structures of AlxGa1-xN films. These results suggest the feasibility of high-efficiency emission in a range of 670 – 900 cm-1 when the devices are positioned in a cavity with high reflectivity of blackbody-like radiation.
Longitudinal optical (LO) phonon has strong electric interaction with particles and fields. Particularly, the interaction in III-nitrides is more significant than that in conventional III-V materials. We show phonon-exciton interaction properties in experimental PL spectrum analysis and theoretical calculation of population transfers of excitonic levels. Thermally nonequilibrium occupations of LO phonons and other modes generated by the LO-phonon decomposition are thought to shift the population distribution in principal quantum number states and kinetic energy to the higher energy side. The radiative exciton recombination lifetime is determined by the population distribution in the excitonic states, which is determined by the balance of the electronic and phononic elementary processes. The interaction of excitons and phonons releases the excess energy to the thermal bath of the lattice system, which sometimes yields negligible lattice temperature increase in the excited region or the nonequilibrium state between electron and phonon systems. A Raman scattering imaging measure is introduced to exhibit spatial transport of phonons generated by the energy relaxation and nonradiative recombination of the excited electrons and holes, where pump-probe measurements are enabled by the simultaneous irradiation of two laser beams. It is found that the phonon transport is blocked by the misfit dislocations located on a Ga0.84In0.16N/GaN heterointerface.
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