Analysis of the modified optical properties and band structure of GaAs1−xSbx-capped InAs/GaAs quantum dots

Abstract

Pronounced Purcell enhancement of spontaneous emission in CdTe/ZnTe quantum dots embedded in micropillar cavities Appl. Phys. Lett. 101, 132105 (2012) Fabrication and photoluminescence of SiC quantum dots stemming from 3C, 6H, and 4H polytypes of bulk SiC Appl. Phys. Lett. 101, 131906 (2012) Radiative transitions in stacked type-II ZnMgTe quantum dots embedded in ZnSe J. Appl. Phys. 112, 063521 (2012) Anomalous temperature dependence of photoluminescence in self-assembled InGaN quantum dots Appl. Phys. Lett. 101, 131101 (2012) Optical properties of multi-stacked InGaAs/GaNAs quantum dot solar cell fabricated on GaAs (311)B substrate J. Appl. Phys. 112, 064314 (2012) Additional information on J. Appl. Phys. The origin of the modified optical properties of InAs/GaAs quantum dots (QD) capped with a thin GaAs 1Àx Sb x layer is analyzed in terms of the band structure. To do so, the size, shape, and composition of the QDs and capping layer are determined through cross-sectional scanning tunnelling microscopy and used as input parameters in an 8 Â 8 kÁp model. As the Sb content is increased, there are two competing effects determining carrier confinement and the oscillator strength: the increased QD height and reduced strain on one side and the reduced QD-capping layer valence band offset on the other. Nevertheless, the observed evolution of the photoluminescence (PL) intensity with Sb cannot be explained in terms of the oscillator strength between ground states, which decreases dramatically for Sb > 16%, where the band alignment becomes type II with the hole wavefunction localized outside the QD in the capping layer. Contrary to this behaviour, the PL intensity in the type II QDs is similar (at 15 K) or even larger (at room temperature) than in the type I Sb-free reference QDs. This indicates that the PL efficiency is dominated by carrier dynamics, which is altered by the presence of the GaAsSb capping layer. In particular, the presence of Sb leads to an enhanced PL thermal stability. From the comparison between the activation energies for thermal quenching of the PL and the modelled band structure, the main carrier escape mechanisms are suggested. In standard GaAs-capped QDs, escape of both electrons and holes to the GaAs barrier is the main PL quenching mechanism. For small-moderate Sb (<16%) for which the type I band alignment is kept, electrons escape to the GaAs barrier and holes escape to the GaAsSb capping layer, where redistribution and retraping processes can take place. For Sb contents above 16% (type-II region), holes remain in the GaAsSb layer and the escape of electrons from the QD to the GaAs barrier is most likely the dominant PL quenching mechanism. This means that electrons and holes behave dynamically as uncorrelated pairs in both the type-I and type-II structures. V C 2012 American Institute of Physics.[http://dx

High efficient luminescence in type-II GaAsSb-capped InAs quantum dots upon annealing

“…3(c) and the right-hand side inset in Fig. 3(a)), The calculated radiative lifetimes (goes as the inverse of the oscillator strength) 23 are 11 ns and 6 ns for samples Sb and Sb-RTA, respectively. These values fit reasonably well with the experimental results.…”

“…3(a)) shows that the potential minimum is split in two parts located outside the QD close to the QD-capping layer interface in the [110] direction, as predicted recently for similar structures. 22,23 The dashed blue line shows the profile along the potential minimum, where the maximum of the probability density of the hole wavefunction is located. If the transition energy for the annealed sample is calculated considering the same QD composition than in the as-grown (0% Ga), a small blue shift of 19 meV is obtained for the fundamental transition energy (see Fig.…”

Impact of the Sb content on the performance of GaAsSb-capped InAs/GaAs quantum dot lasers

“…This hole probability density maximum is split in two regions found at the base of the QD and aligned in the [110] direction. 13,14 Since the built-in electric field in the structure is oriented in the growth direction, it will push the electrons downwards, deeper into the QDs, and the holes upwards towards the top GaAsSb/GaAs interface. This will strongly increase the spatial separation of their wavefunctions and the carrier lifetime and therefore will reduce the oscillator strength, resulting in the observed inhibition of the ground state transition.…”

“…Thus, sample Sb 8 presents a type I band alignment, while sample Sb 18 shows a type II alignment with the hole wavefunction localized outside the QD, in the capping layer. 13 The lasing spectra of the three QDLDs is shown in Fig. 2, where lasing wavelengths of 1072, 1160, and 1164 nm are observed at room temperature for samples Sb 0 , Sb 8 , and Sb 18 , respectively.…”

“…13 While both electrons and holes are mainly injected through the wetting layer in GaAscapped QDs, the presence of the GaAsSb layer would lead to a separate and more efficient injection of carriers: electrons through the wetting layer and holes through the GaAsSb layer. Further experiments are ongoing to demonstrate this point.…”