An atomic scale study on the effect of Sb during capping of MBE grown III-V semiconductor QDs

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.