Molecular beam epitaxial growth and characterization of the vertically aligned InAs quantum dots embedded in Al0.5Ga0.5As

In this paper we describe structural and optical properties of vertically aligned InAs quantum dots (QDs) embedded in Al0.5Ga0.5As. These aligned QDs were grown at 520 degrees C in the Stranski-Krastanow growth mode of molecular beam epitaxy. Measurements by reflection high-energy electron diffraction and atomic force microscopy showed that both the size and density of these QDs increased with the number of stacking periods. The temperature dependence of the wavelength-integrated photoluminescence (PL) intensity revealed that the intense emission from excitons, which dominated the PL spectra at low temperatures, was easily thermally quenched by the large dots in the upper layers. To improve these unfavorable characteristics, we employed a size- and density-controlled growth procedure for the QDs in the upper layers, and succeeded in increasing the PL stability at high temperatures. We also studied a postgrowth annealing treatment for these aligned QD-structures, and round that it is effective to increase the PL intensity when the annealing is performed at around 570 degrees C. By combining the controlled growth procedure with the postgrowth annealing treatment, we realized a strong excitonic emission of which the quenching temperature associated with an activation energy of 0.65 eV was as high as similar to 300 K.