Control of complex quantum structures in droplet epitaxy

Abstract

We report the controllable growth of GaAs quantum complexes in droplet molecular-beam epitaxy, and the optical properties of self-assembled AlxGa 1−x As quantum rings embedded in a superlattice. We found that Ga droplets on a GaAs substrate can retain their geometry up to a maximum temperature of 490 • C during post-growth annealing, with an optimal temperature of 320 • C for creating uniform and symmetric droplets. Through controlling only the crystallisation temperature under As 4 in the range of 450 • C to 580 • C, we can reliably control diffusion, adsorption and etching rates to produce various GaAs quantum complexes such as quantum dots, dot pairs and nanoholes. AlxGa 1−x As quantum rings are also realised within these temperatures via the adjustment of As beam equivalent pressure. We found that crystallisation using As 2 molecules in the place of As 4 creates smaller diameter quantum rings at higher density. The photoluminescence of As 2 grown AlxGa 1−x As quantum rings embedded in a superlattice shows a dominant emission from the quantum rings at elevated temperatures. This observation reveals the properties of the quantum ring carrier confinement and their potential application as efficient photon emitters.

The structural symmetry of nanoholes upon droplet epitaxy

“…Meanwhile, the crystallization at edge of droplets induced by As atoms coming from deposition on the droplet surface and decomposition at the interface produces a circular wall surrounding the droplet, as shown by the schematic diagram in figure 1. A lot of experiments show that the diffusion of As atoms are anisotropic and has preferential orientation in [1][2][3][4][5][6][7][8][9][10] or [110] direction [11,15,41]. Therefore, we conjecture that the gaps in hole sidewall are caused by the anisotropic interface diffusion of As atoms.…”

“…For example, recent study has shown that GaAs/AlGaAs or InGaAs/AlGaAs quantum dots obtained by aluminum (Al) droplet etching exhibit ultra-low multi-photon probability and an unprecedented degree of photon pair entanglement [4][5][6][7], as well as entanglement teleportation [8] and entanglement swapping [9]. During droplet epitaxy, liquid droplets initially form on the substrate surface through a III-column element molecular beam, and an As flux is subsequently used for the crystallization with the droplets into the various III-As nanostructures including quantum dots [10,11], quantum rings [12,13] and nanoholes [14][15][16][17] by controlling the intensity of As flux and the crystallization temperature. The formation mechanism of various nanostructures has been studied by some theoretical models which found that the diffusions of III-column atoms and As atoms determined the final geometry of the nanostructures [18][19][20][21][22][23][24][25].…”

High‐Performance Broadband Tungsten Disulfide Photodetector Decorated with Indium Arsenide Nanoislands

“…Therefore, the In droplets on the surface of WS 2 follow the Volmer–Weber (VW) growth mode without the presence of a wetting layer (WL). [ 21,22 ] The subsequent step is the droplet crystallization by annealing in the group‐V As element atmosphere at 300 °C for 600 s. During this step, the As atoms impinge on the liquid metal droplets and are dissolved into them to form crystal InAs nanoislands. Figure 1b displays a typical atomic force microscopy (AFM) image of the as‐grown InAs nanoislands/WS 2 heterostructure.…”

Independent Control Over Size and Surface Density of Droplet Epitaxial Nanostructures Using Ultra-Low Arsenic Fluxes

“…QD arrays with an ultra-low surface density can be formed by the method of droplet epitaxy [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ], which also has additional advantages over the Stranski–Krastanov growth method. Opportunities provided by droplet epitaxy include the possibility for QD growth without a wetting layer [ 10 , 15 , 16 , 17 ], the fabrication of nanostructures and complexes of nanostructures of various shapes [ 11 , 14 , 17 , 18 , 19 , 20 , 21 ] and QD growth in lattice-matched material systems, such as GaAs/AlGaAs, etc. [ 12 , 16 , 22 , 23 ].…”