Structural and optical studies of vertically aligned InAs/GaAs self-assembled quantum dots

We have investigated interdiffusion and surface segregation in molecular-beam-epitaxially-grown stacked self-assembled InAs/GaAs quantum dots. Using high-resolution cross-sectional scanning tunneling microscopy, we observe lateral variations in the vertical positions of In atoms in both the wetting layers and dot stacks. In some regions, the wetting layer thickness is much less than the dot height, while in other regions, the dot is immersed in the wetting layer. Using In and Ga atom counting, we obtain vertical In-Ga interdiffusion and 1/e segregation lengths of 1.25 and 2.8 nm, respectively. In the dot stacks, significant In-Ga intermixing, primarily due to In surface segregation, is apparent.

We have investigated the effects of in situ and ex situ post-growth thermal annealing on the organization of InAs/GaAs quantum dot superlattices, which consist of regular arrays of InAs islands embedded in GaAs. Using large-scale and high resolution cross-sectional scanning tunneling microscopy, we have mapped out the spatial distributions of the island arrays and the positions of indium atoms located both vertically and laterally between the island arrays. Both in situ and ex situ annealing induce vertical and lateral dissolution of the islands, which in turn significantly affects the organization of the island arrays. Annealing-induced variations in the positions of the indium atoms between the island arrays have enabled us to directly measure indium–gallium interdiffusion and indium segregation lengths. We discuss the effects of residual strain on these processes, which are critical for the design of novel devices based upon semiconductor nanostructures.

Thermally stimulated current in self-organized InAs quantum dots Appl. Phys. Lett. 85, 5604 (2004); 10.1063/1.1832760Self-organized type-II In 0.55 Al 0.45 As/Al 0.50 Ga 0.50 As quantum dots realized on GaAs (311)A High density InAs and In 0.4 Ga 0.6 As dots were grown by molecular beam epitaxy on buried In 0.4 Al 0.6 As and In 0.4 Ga 0.3 Al 0.3 As stressor dots, respectively. Selective radiative recombination was achieved by engineering the band gap of the dots. Structural and luminescence measurements reveal increased size uniformity in the active region dots along with an increase in the dot density. A narrow photoluminescence linewidth of 19 meV was measured at Tϭ17 K.

Effects of seed layer on the realization of larger self-assembled coherent InAs/GaAs quantum dots