Studies of exciton localization in quantum-well structures by nonlinear-optical techniques

Transport of superradiant excitons in GaAs single quantum wells

“…Lower in the resonance, however, T 2 is larger, an effect reported earlier by Hegarty and Sturge, 26 and attributed to localization: For the 50-Å SQW, we observe T 2 ϭ25 ps. For the 35-Å SQW the elongation is even more pronounced.…”

“…From this we conclude that the free-exciton picture fails, and that excitons localize in the low-energy wing, in agreement with earlier findings. 18,26 B. High N ex and T, transport and dephasing By increasing the excitation density N ex and temperature T, we can study the dephasing and transport properties of REE in the presence of interaction.…”

Effect of temperature on the optical properties of GaAsSbN/GaAs single quantum wells grown by molecular-beam epitaxy

“…16 -20 Several studies have shown that in QW heterostructures, random fluctuations of the alloy composition and roughness of the barrier-well interfaces are determinant factors of sample quality. [21][22][23][24] These defects create fluctuations in the confinement potential and lead to the formation of a band tail in the excitonic density of states. 18,[23][24][25] Depending on the energy excess ͑obtained from the laser pumping energy͒ and the magnitude of the potential fluctuation, the excitons will relax either to the local minima or to the absolute minimum of the confinement potential via phonon emission before the radiative recombination takes place.…”

Distribution of oscillator strengths for recombination of localised excitons in two dimensions

“…This is shifted toward lower energies because the exitons can lose energy before they decay. Time-resolved studies of spectral hole burning indicate that the energies of excitons can change over a timescale of typically tens of picoseconds, much shorter than the half-life for decay of excitons, typically several hundred picoseconds [5,6]. The predominant mechanism of energy loss for the excitons appears to be by the excitation of phonons: if the absorption spectrum is probed with narrow spectral lines, it is possible to observe features in the luminescence spectrum which are shifted from the probe frequency by multiples of the frequency of the optical phonons [6].…”

“…The excitons are able to interact with phonons by radiationless processes [5,6], becoming trapped in local minima of the confinement energy: the lifetime for electron-hole recombination is typically long enough that most of the luminescence observed from these samples is from trapped excitons. This trapping effect has recently been observed directly by spatially resolved studies of exciton luminescence [7,8]: if the luminescence is recorded from a macroscopic area of the sample, a broad spectrum is observed, whereas sufficiently small microscopic areas show either no luminescence, or a small number of relatively sharp lines, corresponding to excitons in a single trap.…”