Self-assembly of laterally aligned GaAs quantum dot pairs

Abstract

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.

Precise shape engineering of epitaxial quantum dots by growth kinetics

“…7(b)] [23,52]. In between these two extremes, more complex morphologies, such as double rings and molecules, can be obtained [30,35,37,40].…”

“…The As pressure and substrate temperature during crystallization are used to control nanostructure morphology [30,35,37,40]. Three sets of samples (P , T , and V ) were grown in this study.…”

“…A III-column element molecular beam is initially supplied for the formation of droplets on the substrate surface in vacuum, and subsequently an As flux is used for the crystallization of droplets into the III-As nanostructures. With a suitable selection of growth conditions, and by carefully controlling the group-III crystallization kinetics into a III-V semiconductor, it is possible to engineer the final shape of the nanocrystals from islands [25,[27][28][29], rings [30,31], wires [32,33], and even more complex structures [34][35][36][37][38][39].…”

Structural and optical properties of position-retrievable low-density GaAs droplet epitaxial quantum dots for application to single photon sources with plasmonic optical coupling

“…The droplet epitaxy (DE) method has the merit of the growth of various quantum structures, such as quantum rings, disks, coupled QDs, and concentric quantum double rings, as well as low-density QDs, due to a perfect separation of groups 3 and 5 [12][13][14][15]. In addition, larger GaAs DE QDs can be grown on AlGaAs without strain effect, for larger oscillation strength, compared with InAs QDs on GaAs.…”

Quantum Dots Prepared by Droplet Epitaxial Method

“…With the modified DE method, aligned QD pairs and QD molecules can be produced without involving lithographic technology [14,15].…”