We report the fabrication of self-assembled, strain-free GaAs/Al0.27Ga0.73As quantum dot pairs which are laterally aligned in the growth plane, utilizing the droplet epitaxy technique and the anisotropic surface potentials of the GaAs (100) surface for the migration of Ga adatoms. Photoluminescence spectra from a single quantum dot pair, consisting of a doublet, have been observed. Finite element energy level calculations of a model quantum dot pair are also presented.When two semiconductor quantum dots (QDs), which can each spatially confine an individual carrier in a discrete energy level, are in close proximity to each other, these carriers begin to interact with each other. Specifically, the wavefunctions of the carriers confined in each QD of the QD pair (QDP) begin to overlap, resulting in an efficient carrier tunneling [1,2], and the wavefunctions may become admixed to form molecular orbital states. Moreover, resonance in the optical transition energies leads to the formation of a coupled QDP via dipole-dipole interactions [3,4,5]. Proposals for using such a coupling in quantum information processing have been brought forth [6,7]. To this end, various semiconductor QDPs have been fabricated and studied, such as coupled QDs grown by cleaved edge quantum well overgrowth [1], vertically-aligned QDs grown by StranskiKrastanow epitaxy incorporating an indium-flush procedure [2,4], and interface QDs formed in a quantum well [3]. In this work we demonstrate the fabrication of self-assembled, laterally aligned GaAs/Al 0.27 Ga 0.73 As QDP structures by droplet epitaxy: Droplet epitaxy is a nonconventional growth technique for the self-assembly of high quality nanostructures with lattice-matched materials, making possible the growth of nanostructures with various structural characteristics, such as QDs [8,9,10], quantum rings (QRs) [11], and concentric double QRs [12,13]. Here we observe the formation of laterally aligned GaAs QDPs by accurately selecting the As 4 flux during crystallization. Within relevant conditions, the nanocrystals show a remarkable shape like a double summit, reflecting the anisotropic surface potentials of the GaAs (100) surface. To gain insight into the interactions between the carriers confined in such a structure, we study the QDP single-structure optical properties. We further consider the electronic structure of a model QDP via energy level calculations requiring no inclusion of strain.The samples are grown by droplet epitaxy using a molecular beam epitaxy system with elemental sources and a valved As source, which enables the accurate control of the As 4 flux.
