The role of wetting layer states on the emission efficiency of InAs/InGaAs metamorphic quantum dot nanostructures

Abstract

We report on a photoluminescence and photoreflectance study of metamorphic InAs/InGaAs quantum dot strain-engineered structures with and without additional InAlAs barriers intended to limit the carrier escape from the embedded quantum dots. From: (1) the substantial correspondence of the activation energies for thermal quenching of photoluminescence and the differences between wetting layer and quantum dot transition energies and (2) the unique capability of photoreflectance of assessing the confined nature of the escape states, we confidently identify the wetting layer states as the final ones of the process of carrier thermal escape from quantum dots, which is responsible for the photoluminescence quenching. Consistently, by studying structures with additional InAlAs barriers, we show that a significant reduction of the photoluminescence quenching can be obtained by the increase of the energy separation between wetting layers and quantum dot states that results from the insertion of enhanced barriers. These results provide useful indications on the light emission quenching in metamorphic quantum dot strain-engineered structures; such indications allow us to obtain light emission at room temperature in the 1.55 microm range and beyond by quantum dot nanostructures grown on GaAs substrates.

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

“…The QD effective recombination rate (r i ) is composed by the sum of radiative and non-radiative terms. The QD radiative recombination rate is obtained from the inverse of the measured PL decay time at 10 K. The activation energy of the thermal carrier capture into defect states has been set to $20 meV, 25,26 The main output parameter is the energy dependent i values plotted in Figure 7(a). We observe how i decreases with the QD size in both samples with almost the same trend, reflecting the carrier escape character.…”

“…It has been investigated attending to the available final states, i.e., QD excited states, 15,21 wetting layer, 4,6,7,13,20,22 GaAs barrier, 8,9,23 and impurity/defect levels. [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.…”

Time resolved emission at 1.3 μm of a single InAs quantum dot by using a tunable fibre Bragg grating

“…In this regard, several strategies for improving the operational temperature of SAQDs have been reported, such as the addition of InAlAs barriers during the epitaxial growth of InAs QD to raise the activation energy of the carrier thermal escape [3] or the single photon emission at 45 K with small InP/GaInP QDs [4]. Regarding this important design parameter, there are some growth strategies to obtain QDs samples emitting at the second or third telecommunication windows.…”

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

“…It has already been shown that the In content in the barrier has a direct influence on the emission properties of QDs, such as the emission energy and the energy barrier for thermal escape of confined carriers. 6,8 In this paper, it is demonstrated that, when the In concentration in pseudomorphic UCLs increases above a certain threshold (x ! 0.20), the exciton dynamics changes in a way that is consistent with the introduction of non-radiative recombination centres in the UCL.…”

“…[1][2][3] InAs/GaAs structures with a few QDs/lm 2 and emission at 1.3 lm have been successfully prepared by using epitaxial growth conditions that result in large cation migration length [4][5][6] and by growing pseudomorphic InGaAs upper confining layer (UCL) on top of the QDs. 6,7 A complete picture of QD properties in this type of structures is necessary in order to correctly describe carrier dynamics that strongly depends on peculiar characteristics of the structures such as the energy of excited states and wetting layer (WL), 8 the presence of defects and non-radiative recombination centers 9,10 and also the existence of bimodal QD size distributions. 11 The results of this work, concerning the use of high lattice-mismatched UCL, are of interest also for the realization of structures that employ complex capping layers to engineer the properties of QDs, such as infrared photodetectors 12 and QDs in a well structures.…”