Growth and properties of the MOVPE GaAs/InAs/GaAsSb quantum dot structures

Abstract This review paper summarizes some of results achieved during last years of our quantum dot (QD) research. We show that the QD shape (aspect ratio and elongation) significantly influences the QD photoluminescence (PL) spectrum. Magnetophotoluminescence can be used for determination of the anisotropy of QDs. While the calculated shifts in magnetic field of the energies of higher radiative transitions are found to be sensitive to the lateral elongation, the shift of the lowest transition is determined mainly by the exciton effective mass. This behavior can be used for determining both the effective mass and the elongation fairly reliably from the magnetophotoluminescence spectra displaying at least two resolved bands. Lateral shape of InAs/GaAs QDs in vertically correlated structures was also studied. We found the ways to control the QD elongation and consequently the energy difference between PL transitions by adjusting properly the spacer layer thickness. The main goal was to redshift QD PL emission towards telecommunication wavelengths of Metal Organic Vapor Phase Epitaxy prepared InAs/GaAs QDs using InGaAs or GaAsSb covering strain reducing layer (SRL). Our results proved that GaAsSb SRL improves the QD PL properties and the type I or type II band alignment can be controlled by both, GaAsSb composition and QD size. Maintaining the type I heterostructure is important for high luminescence efficiency and emission wavelength stability of QD structure. The simulation of electron structure in InAs QDs covered with GaAsSb SRL and experimental results reveal the importance of increasing QD size for obtaining a longer wavelength PL from the type I heterostructure. The type II structure of InAs/GaAs QDs covered by GaAsSb SRL with Sb content near 30% enabled us to achieve extremely long emission wavelength at 1.8 µm. The high amount of antimony in the SRL causes the preservation of QD size, and increased QD size prolongs the PL wavelength. The type II heterostructures with ground state electrons confined in InAs QDs and ground state holes in GaAsSb SRL have a strong potential in detector and solar cell applications as is demonstrated by photocurrent measurement. The dependence of built in electric field on QD PL properties is presented since this knowledge is necessary for application of QDs in different kind of electronic structures. We have experimentally demonstrated that the type I/type II transition of band structure of InAs QD with GaAsSb SRL does not depend only on the composition of the SRL, but also on other structure parameters, like QD size or intensity of electric field.