Thermal activation of excitons in asymmetric InAs dots-in-a-well InxGa1−xAs∕GaAs structures

Abstract

Photoluminescence, its temperature dependence, and photoluminescence excitation spectra of InAs quantum dots embedded in asymmetric InxGa1−xAs∕GaAs quantum wells [dots in a well (DWELL)] have been investigated as a function of the indium content x (x=0.10–0.25) in the capping InxGa1−xAs layer. The asymmetric DWELL structures were created with the aim to investigate the influence of different barrier values at the quantum dot (QD)/quantum well interface on the photoluminescence thermal quenching process. The set of rate equations for the two stage model for the capture and thermal escape of excitons in QDs are solved to analyze the nature of thermal activation energies for the QD photoluminescence quenching process. The two stage model for exciton thermal activation was confirmed experimentally in the investigated QD structures as well. The localization of nonradiative defects in InAs∕InGaAs DWELL structures is discussed on the base of comparison of theoretical and numerically calculated (fitting) results.

Size dependent carrier thermal escape and transfer in bimodally distributed self assembled InAs/GaAs quantum dots

“…[23][24][25][26] Thermal escape can be also investigated attending to the nature of the particles being promoted to a higher energy state. 14 Depending on the model, the correlated (excitonic escape), 6,8,10,12,23 the uncorrelated electron-hole pair (ambipolar escape), 4,9,14 or just one of the carriers (unipolar escape) 15 can be considered. Whether one or the other is appropriate in a particular sample depends on the barrier height and therefore might vary for QDs of given composition but different size.…”

“…A variety of carrier redistribution effects caused by temperature has been investigated in QD ensembles. [4][5][6][7][8][9][10][11][12][13][14][15] It is commonly accepted that the sigmoidal evolution of the peak energy and full width at half maximum of the PL bands is due to carrier promotion from small QDs to larger ones. 6 Therefore, quantum dot size distributions, carrier capture, relaxation, and re-trapping among QDs of different sizes had to be considered to model correctly the QD recombination dynamics.…”

The effect of high-In content capping layers on low-density bimodal-sized InAs quantum dots

“…The observed Arrhenius dependence would be accounted for by two activation energies, as commonly observed in similar QD structures. 26,[36][37][38][39] The sharp decrease of the PL intensity corresponds to a large activation energy (200-400 meV) that depends on the barrier composition (see Tables I and II); the energy difference is consistent with the thermionic electron-hole escape from QD to the WL/WL-QW (for UCL structures).…”

“…This behavior has been already observed in similar structures and it has been justified by different hypotheses including resonant energy levels between different families, 40 losses of carriers from the WL to the GaAs, 26,36 losses within the barrier itself, 38,39 or losses related to defects. 8,11,37 With the exception of the structure with x ¼ 0.30, three regions can be distinguished in the temperature variation of the recombination time in all samples for QD1 (Fig.…”

“…25, we studied the structural and optical properties of WLs and QWs of these structures and we showed that, while for low In contents, the heavy hole wavefunction is confined close to the lower GaAs/InGaAs interface, for the x ¼ 0.30 structure, both the electron and hole wavefunctions are delocalized over the entire UCL. As a consequence, we can infer that the presence of compositionally graded interfaces and alloy disorder in the UCL, which increase with In content, 26 should have a greater influence on the x ¼ 0.30 structure than on the other ones. Then, this is a possible explanation for the increase of the WL-QW emission linewidth.…”