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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.

We report low-temperature photoluminescence measurements on highly-uniform GaAs/AlxGa1−xAs quantum dots grown by droplet epitaxy. Recombination between confined electrons and holes bound to carbon acceptors in the dots allow us to determine the energies of the confined states in the system, as confirmed by effective mass calculations. The presence of acceptor-bound holes in the quantum dots gives rise to a striking observation of the phonon-bottleneck effect.

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