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Type II emission optoelectronic devices using GaAsSb strain reduction layers (SRL) over InAs quantum dots (QDs) have aroused great interest. Recent studies have demonstrated an extraordinary increase in photoluminescence (PL) intensity maintaining type II emission after a rapid thermal anneal (RTA), but with an undesirable blueshift. In this work, we have characterized the effect of RTA on InAs/GaAs QDs embedded in a SRL of GaAsSb by transmission electron microscopy (TEM) and finite element simulations. We find that annealing alters both the distribution of Sb in the SRL as well as the exchange of cations (In and Ga) between the QDs and the SRL. First, annealing causes modifications in the capping layer, reducing its thickness but maintaining the maximum Sb content and improving its homogeneity. In addition, the formation of Sb-rich clusters with loop dislocations is noticed, which seems not to be an impediment for an increased PL intensity. Second, RTA produces flatter QDs with larger base diameter and induces a more homogeneous QD height distribution. The Sb is accumulated over the QDs and the RTA enlarges the Sb-rich region, but the Sb contents are very similar. This fact leaves the type II alignment without major changes. Atomic-scale strain analysis of the nanostructures reveal a strong intermixing of In/Ga between the QDs and the capping layer, which is the main responsible mechanism of the PL blueshift. The improvement of the crystalline quality of the capping layer together with higher homogeneity QD sizes could be the origin of the enhancement of the PL emission. [ABSTRACT FROM AUTHOR]

The use of Sb during the capping process of quantum dots (QDs) to tune the emission wavelength has been investigated by means of cross-sectional scanning tunneling microscopy (X-STM), photoluminescence (PL) measurements and atomic force microscopy. It is found that a capping layer of GaAsSb reduces InAs/GaAs QD decomposition during capping due to the smaller lattice mismatch with the QD and due to the surfactant effect of Sb. An Sb content of 14% in the GaAsSb layer has been found to be sufficient to eliminate the QD decomposition completely and improve the PL properties. Further increase in the Sb content causes a degradation of the PL properties. Reduction of the QD decomposition has also been achieved by soaking the QDs with Sb before the capping. Furthermore, it is shown that the segregation of In and of Sb in the Ga and the As sublattices respectively are two independent processes. Similar investigations to the use of Sb to tune InAs/InP (311B) QDs are reported. Also in this case, the use of Sb, either in the form of elemental Sb or as a GaAsSb alloy, has resulted in elimination of QD decomposition. [ABSTRACT FROM AUTHOR]