Large-kexciton dynamics in GaN epilayers: Nonthermal and thermal regimes

Abstract

We present a detailed investigation concerning the exciton dynamics in GaN epilayers grown on c-plane sapphire substrates, focussing on the exciton formation and the transition from the nonthermal to the thermal regime. The time-resolved kinetics of LO-phonon replicas is used to address the energy relaxation in the excitonic band. From ps time-resolved spectra we bring evidence for a long lasting non-thermal excitonic distribution which accounts for the first 50 ps. Such a behavior is confirmed in different experimental conditions, both when non-resonant and resonant excitation are used. At low excitation power density the exciton formation and their subsequent thermalization is dominated by impurity scattering rather than by acoustic phonon scattering. The estimate of the average energy of the excitons as a function of delay after the excitation pulse provides information on the relaxation time, which describes the evolution of the exciton population to the thermal regime.

Long-living nonlinear behavior in CsPbBr3 carrier recombination dynamics

“…In fact, at 45 K the bound exciton emission becomes negligible with respect to the free exciton contribution, and by the high energy tail of quasi resonantly excited PL spectra, at 10 K, we extract a carrier temperature lower than 20 K (not shown). As expected from the model discussed in [28,29], T ∞ should correspond to the lattice value (i.e. 10 K), but TR-PL spectra up to a delay of 1.5 ns show a temperature (T ≈ 30 K) still above that of the lattice, indicating the presence of a very slow process.…”

“…Given the excitation density and the time resolution of our experiments, the thermalization regime that we investigated is dominated by the interaction of the carriers with acoustic phonons. In this case, the time evolution of T eff can be reproduced by [28]:…”

Exciton radiative lifetime in transition metal dichalcogenide monolayers

“…Non-linear techniques such as Four Wave mixing experiments in high quality samples will be highly desirable to extract this fundamental parameter 66 . After a few tens of ps, these fast exciton-phonon interactions will yield the establishment of a thermalized Boltzmann distribution of exciton and as a consequence longer radiative recombination times 45,60,67 .…”

Low-temperature carrier transport across InGaN multiple quantum wells: Evidence of ballistic hole transport

“…Hence, the critical phenomenon leading to the fast rise and large intensity of the deep QW PL is the transport of holes. Here one should bear in mind that the experimentally determined transfer time (PL rise time) is significantly shorter than the exciton formation time of ∼10 ps [9,10], which means that electrons and holes travel toward the deep QW as free carriers.…”