Time-resolved photoluminescence studies of free and donor-bound exciton in GaN grown by hydride vapor phase epitaxy

Abstract

Time-resolved photoluminescence (PL) spectroscopy was used to study the radiative recombination of free and donor-bound excitons in unintentionally doped GaN grown by hydride vapor phase epitaxy. Low temperature (4 K), time-integrated PL spectra identified the free exciton (A), the donor-bound exciton peak ∼6 meV below, and the acceptor-bound exciton ∼20 meV below the free exciton peak. A radiative recombination lifetime of 295 ps for the free exciton and 530 ps for donor-bound exciton were found at 4 K. The decay of the free exciton remained single exponential to room temperature, with an increase in lifetime to 530 ps, consistent with the thermal excitation of exciton states.

Surface related and intrinsic exciton recombination dynamics in ZnO nanoparticles synthesized by a sol-gel method

“…Therefore, the exciton redistribution in momentum space changes as lattice temperature increases, giving rise to a successively smaller electron-hole population, which fulfills the momentum conservation requirement for recombination, and hence the radiative recombination lifetime increases with temperature. 25 In conclusion, the size dependence of the UV photoluminescence spectra of various QD sizes has provided an evidence for the quantum confinement effect. The UV emission near the band edge is attributed to the free exciton emission, and the green emission is originating from surface defects.…”

Transient photoluminescence of shallow donor bound excitons in GaN

“…The above data for the DBE transients in GaN together with previous work [17][18][19][20][21] demonstrate that an evaluation of the no-phonon DBE PL transient with above band-gap excitation does not in general give relevant data for the radiative lifetime r of these processes. Obviously the obtained transients fail to demonstrate a purely exponential decay, and the initial part of this decay corresponds to a much faster process than the radiative DBE decay in the bulk of the material.…”

“…In most cases the decay time in previous work has been evaluated either as an exponential fit to the initial part of the NP DBE decay, or an average over the part of the NP transient that has been measured. 12,[17][18][19][20][21] To get a reliable value of the r parameter the real bulk recombination has to be monitored. This can be done as in this work if various replicas like TETs occurring in the transparent region of the spectrum are monitored.…”

“…TRPL data for bound and free excitons ͑FEs͒ in GaN have been reported in a large number of papers over the last decades, with quite a large variation in the results. [17][18][19][20] The low-temperature DBE decay times reported in thin GaN layers grown on foreign substrates are typically very short ͑Ͻ300 ps͒, related to the large defect concentrations in these samples. 17 The corresponding FE decay times are then invariably very short as well ͑Ͻ100 ps͒.…”

Strain variation with sample thickness in GaN grown by hydride vapor phase epitaxy

“…The D ‫ؠ‬ ,X lifetime is greater than the free exciton lifetime as is usually observed. [13][14][15] The lifetime increases with sample thickness, as the surface strain decreases. This suggests that the factors contributing to strain also introduce recombination paths as well as nonradiative decay processes.…”