Propriedades ópticas de pontos quânticos empilhados de InAs/GaAs

Abstract

The technological advances that have taken place in recent years have made it possible to study and manufacture structures with smaller dimensions. In this scenario, one area that is attracting great interest in the present time is the study of quantum dots (QD's) - due to its possibilities of application, its structural properties and the electronic structure of the load carriers confined. There are a large number of possible applications for quantum dots, such as: solar cells, detectors, lasers, televisions, biomedical etc. The most studied quantum dots are generated by the method called Stranski-Krastanov (SK). This technique allows to produce quantum dots that are self-organized islands that arise because of the difference between the network parameters of the epitaxial layers and the substrate used. The use of this technique presents interesting favorable points such as high emission efficiency, better discretization of energy levels and greater area density. Self-organized quantum dots present another important property that is the possibility of the growth of aligned multilayers of stacked quantum dots due to the self alignment phenomenon. The growth of quantum dots from the SK method presents as main difficulty the control of the size and distribution of the islands in the sample. Recent studies indicate that the growth of samples with vertically stacked layers and separated by semiconductor material allows the appearance of quantum dots with more uniform sizes in the upper layers. In this work, a set of 5 self-organized InAs /GaAs double QDs samples grown by the SK method on GaAs substrates with GaAs spacer layers of different thicknesses was studied. The following techniques were used to study the optical properties of the samples: Photoluminescence (PL) and Magneto-Fotoluminescence. From the analysis of the data obtained, it was verified that the samples presented typical behaviors for QDs. The variation of the thickness of the spacer layer of each sample demonstrated the occurrence of a competition between the effects of electronic coupling and In/Ga intermixing. It was verified that the temperature increase caused the displacement of the observed peaks to regions of lower energy and decrease in their intensity. It was found that the position of the peaks was not significantly altered as a function of the power variation; however, the decrease in the excitation power caused the decrease of peak intensity. Measurements of photoluminescence performed under magnetic field variation indicated the occurrence of Strain reinforcing the occurrence of intermixing. In addition, the occurrence of spin polarization was also observed for the samples.