Exciton-phonon interactions, exciton binding energy, and their importance in the realization of room-temperature semiconductor lasers based on GaN

Abstract

Temperature dependence of the linewidths of free-exciton A and B transitions was investigated. Experimental linewidths were fitted to a theoretical model considering various interactions of excitons with phonons in addition to inhomogeneous broadening. It was shown that acoustic phonon scattering must also be considered to explain the emission linewidth broadening, in contrast to a recent report on luminescence linewidths in GaN. These exciton-acoustic-phonon interactions also explain the fast energy relaxation of free excitons to the bottom of the exciton band, which leads to generally observed short free-exciton lifetimes in GaN. The exciton-longitudinal-optical ͑LO͒ -phonon coupling constant was found to be extremely large. This was explained as being due to the Fröhlich interaction and the polar nature of GaN. The binding energy of both A and B excitons was found to be 26 meV. The relevance of exciton-phonon interactions and the binding energy of free excitons in achieving room-temperature exciton-based semiconductor lasers was discussed. Though exciton-LO-phonon interaction was very strong in GaN, it was still possible to observe room-temperature excitons since the exciton binding energy is very large.

Excitons versus free charges in organo-lead tri-halide perovskites

“…15) we can neglect exciton-exciton interaction, which only occurs for n410 20 cm À 3 , because there is essentially no wavefunction overlap. Consequently, we can safely assume that the binding energy is independent of excitation density 23,25 . Within such an approximation, we can apply the law of mass action for Wannier-Mott excitons, as described by the Saha-Langmuir equation 13,14 .…”

“…The coherence lifetime T 2 of the excited state transition can be affected by the natural population decay of the excited state (T 1 ) and by elastic scattering events (with rate g) that do not change the excited state population but contribute to the broadening of the transition. For most polar inorganic solids at high temperatures (for example, T4100 K), phonon interaction leads predominantly to exciton ionization (through inelastic ARTICLE scattering) 22,23 . This approximation is valid in our case, as the exciton absorption broadening occurs together with a reduction in the intensity of the optical excitonic transition, thus the population decay rate, 1/T 1, can be described as the sum of an intrinsic decay rate (k 0 ) and thermal dissociation rate (k T ) 22 …”

Intrinsic dynamics of weakly and strongly confined excitons in nonpolar nitride-based heterostructures

“…Under high excitation densities, scattering between center-of-mass quantized excitons extends their distribution in k-space until scattered excitons gain enough energy to relax through the emission of an LO phonon. As the latter mechanism is much more efficient than relaxation through the emission of acoustic phonons, 55 the whole population of center-of-mass quantized excitons relaxes more efficiently. Under high excitation conditions, the emission from the fundamental confined state at 3.474 eV is thus promoted compared to the higher-energy modes at 3.478, 3.483, and 3.486 eV.…”

Plasma-Assisted MBE Growth of GaN on HVPE-GaN Substrates

“…2a, has a narrow near band edge peak at 363 nm (3.42 eV) and the broad yellow luminescence around 600 nm. When measured at 9 K only the near band edge peak at 356 nm is present, matching the position of the free exciton according to Viswanath et al [5] although the experimental resolution is insufficient to make a positive identification. The doped n-GaN sample is shown in Fig.…”