Strain Effects on Optical Properties of (In,Ga)As-Capped InAs Quantum Dots Grown by Molecular Beam Epitaxy on GaAs (113)A Substrate

We have investigated the optical properties of InAs/GaAs (113)A quantum dots grown by molecular beam epitaxy (MBE) capped by (In,Ga)As. Reflection high-energy electron diffraction (RHEED) is used to investigate the formation process of InAs quantum dots (QDs). A broadening of the PL emission due to size distribution of the dots, when InAs dots are capped by GaAs, was observed. A separation between large and small quantum dots, when they are encapsulated by InGaAs, was shown due to hydrostatic and biaxial strain action on large and small dots grown under specifically growth conditions. The PL polarization measurements have shown that the small dots require an elongated form, but the large dots present a quasi-isotropic behavior. 1. Introduction Self-assembled quantum dots (QDs) have been studied intensively for more than a decade due to their unique physical properties arising from the three-dimensional quantum confinement of carriers and delta-like density of state [1–3]. QDs find many applications in optoelectronic devices [2, 3], delivering a striking improvement of the performance over conventional technology. However, the stochastic nature of the QDs makes it difficult to obtain dots with uniformity in both their size and their spatial distribution, which constitute the most dramatic problem that prevents the production of optoelectronic devices with a high quality of dots since it is incompetent to provide the prospect of temperature-independent low-threshold lasers [4, 5]. The structural and optical properties strongly depend on growth conditions, such as growth temperature, growth rate, and the capping layer material. One way to improve or adjust the QDs properties is the utilization of high-index substrates which exhibit some interesting phenomena, with respect to (001) orientation. To date, there are few reports about successful growth of self-organized QDs on high-index substrates, comparable to those with (001) orientation [6, 7]. Growth studies have also been realized with the intention of controlling size, shape, and density of the QDs [8]. The growth control and the valid results, obtained on these structures, which are elaborated on high-index substrates, have permitted to improve optical and electrical properties of many compounds [9, 10]. Prior to understanding how the capping layer influences the transition energies of [11？ ] grown InAs QDs, one has to know the effect on the transition energies of QD growth on [11？ ] substrates ( ). The origin of the variation of the transition energy with the substrate orientation can be traced back