Two-dimensional exciton dynamics and gain formation processes inInxGa1−xNmul

Abstract

We investigated exciton dynamics in In x Ga 1Ϫx N multiple quantum wells at 2 K and room temperature by means of time-resolved photoluminescence and pump-and-probe measurements. Under low excitation density, the temporal change of the spontaneous emission indicated slow dynamical features of the two-dimensional exciton localization, while, above a stimulation threshold density, the decay time of the emission was shortened to be less than ϳ30 ps due to the stimulated emission process. Further, the time-resolved pump-and-probe measurement revealed a fast relaxation of photoexcited delocalized electron-hole (e-h) pairs into localized states. Above stimulation threshold, localized states were saturated, and e-h pairs at delocalized states were observed. Two-dimensional e-h pairs at delocalized states relaxed into localized states and excitons were formed, from which the optical gain was formed in terms of the stimulated emission process. ͓S0163-1829͑99͒13047-9͔

Ultrafast carrier relaxation in GaN,In0.05Ga0.95N,and anÖzgür1, Everitt2 2003Phys. Rev. B

“…Similar non-degenerate TRDT measurements have been performed on GaN, 22,23 InGaN epilayers 8,9 , and InGaN MQWs 9,10,11,24 , by different groups. These studies provide insights on important aspects of carrier relax- ation dynamics.…”

“…10,11,24 After SE ends (5 -10 ps), the carriers at the QW band edge recombine only through SPE, and carriers at higher energies relax at a similar rate to replace those lost at the QW band edge. For all excitations this is observed as the redshift of the bleaching.…”

“…SE decay times faster than 10 ps have been observed for similar MQW structures at room temperature and at 2 K. 11,24 In one study, a three-level rate equation model was also developed, consisting of 2D QW, 3D barrier, and ground (recombined) states. 11 This model suggested that the fast relaxation was due to carriers decaying from the 3D states to refill the 2D states emptied by SE. The fact that higher energy 3D states supply carriers to lower energy states undergoing SE has been confirmed in the GaN (Fig.…”

“…In addition to many studies on recombination times, 5,6,7 there have been a limited number of reports on ultrafast carrier dynamics in InGaN heterostructures 8,9 and multiple quantum wells (MQW). 10,11 Measurements on heterostructures, single QWs, and MQWs have emphasized different aspects of carrier relaxation in nitrides. In this paper, we report comprehensive room temperature ultrafast measurements on a bulk GaN, an InGaN epilayer, and an InGaN MQW sample having barriers with the same In composition as the epilayer sample.…”

Excitonic field screening and bleaching in InGaN/GaN multiple quantum wells

“…As demonstrated in piezoelectric materials, ultrafast differential transmission spectroscopy can extract the needed carrier transport and recombination dynamics by separating the field screening behavior from the band-filling effects [8]. A few differential transmission measurements on InGaN/GaN QWs that have focused on stimulated emission processes and carrier capture times have been reported [15][16][17]. However, of those experiments, none has spectrally and temporally resolved the resulting changes in absorption coefficient due to in-well field screening.…”