Electronic Structure of Strained GaSb/GaAs Quantum Dot: Tight-Binding Approach

Abstract

GaSb quantum dots (QDs) in a GaAs matrix have attracted much attention for the potential ability to extend the accessible wavelength of QD emitters towards a wavelength of > 1.3 μm owing to their unique electronic and optical properties caused by their staggered (type-II) band alignment. North et al. calculated the electronic structure of self-assembled GaSb/GaAs dots by using the simple one-band model (effective mass model). Therefore it is interesting to carry out the detailed calculations using a more accurate method, in particular in the view of the new experiments. The aim of this work is to study the electronic properties of GaSb/GaAs self-assembled quantum dots (SAD) by using the sp 3 s * empirical tight-binding method. The influence of strain on the electronic structure is determined by minimizing the elastic energy within the Valence Force Field Approach and the piezoelectric potential is calculated by solving the corresponding 3D Poisson equation. Single-particle bound-state energies are computed as a function of the dot sizes. Finally we have found that the theoretical PL spectra are in a good agreement with the experiment and k.p method. empirical models are widely implemented to study a large quantum dots. There are three empirical models, the k.p approximation (9), the pseudopotential model (10) and the tight-binding model (11), (12). The k.p approximation treats a quantum dot as a confined bulk and continuum system, while the pseudopotential and tight-binding models treat the system with the atomistic description. The distinction between the two atomistic models is the degree of atomic detail included in the model. Within the tight-binding model, the atomistic detail is limited to a small basis set, while in the pseudopotential model the feature of wave functions is described with a large basis set. Therefore the tight-binding model is computationally less costly than the pseudopotential model. The tight-binding model is a good candidate for the study of relatively big and complicated systems. At the moment, the theoretical calculations of the type-II quantum dots have not been extensively investigated and there are only few papers that we can mention here. North and co-authors (13) investigated the electronic structure of type-II GaSb/GaAs quantum dots by using the multiband effective-mass calculation. K. Gradkowski and et al. (2) reported the results of the room temperature photoreflectance (PR) and photoluminescence (PL) measurements of molecular beam epitaxy (MBE) grown GaAsSb/GaAs quantum dot structure: one with a capping quantum well and one without it. PL technique is employed to probe the ground-state transition energies. Using the experimental data, they calculated a band structure of these dots by using the 8-band k.p approach. The theoretical analysis accounts well in both GaAsSb/GaAs quantum dot with a capping quantum well and one without it. In this paper, we report the tight-binding calculations of the type-II GaSb/GaAs quantum dots. The strain distribution of the quantum dot is calculated by using the Valence Force Field method. The piezoelectricity is also obtained by solving the 3D Poisson's equation. Then we numerically calculate the electronic structure of the quantum dot as a function of the dot sizes. Finally we compare our calculated results with the experiment and another numerical analysis.