In this paper, we report the effect of Au thickness on the self-assembled Au droplets on GaAs (111)A and (100). The evolution of Au droplets on GaAs (111)A and (100) with the increased Au thickness progress in the Volmer-Weber growth mode results in distinctive 3-D islands. Under an identical growth condition, depending on the thickness of Au deposition, the self-assembled Au droplets show different size and density distributions, while the average height is increased by approximately 420% and the diameter is increased by approximately 830%, indicating a preferential lateral expansion. Au droplets show an opposite evolution trend: the increased size along with the decreased density as a function of the Au thickness. Also, the density shifts on the orders of over two magnitude between 4.23 × 1010 and 1.16 × 108 cm−2 over the thickness range tested. At relatively thinner thicknesses below 4 nm, the self-assembled Au droplets sensitively respond to the thickness variation, evidenced by the sharper slopes of dimensions and density plots. The results are systematically analyzed and discussed in terms of atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), cross-sectional surface line profiles, and Fourier filter transform (FFT) power spectra.

We demonstrate low-density quantum dot molecules (QDMs) by selective etching using In droplets as a mask. Selective etching is performed with InGaAs QDMs buried underneath GaAs capping layer, on which In droplets are formed by droplet epitaxy using molecular beam epitaxy. During the chemical etching, the droplets act as a mask and QDMs underneath the droplets that only survive. Photoluminescence measurement from the selectively etched QDMs in mesa structures shows a much reduced intensity, which indicates low-density QDMs. This technique provides a simple and flexible method to attain low-density QDMs. The density can be easily modified by the control of the size and density of In droplets, which is suitable for single QDM spectroscopy and for their device applications.Index Terms-Atomic force microscopy (AFM), droplets, low density, molecular beam epitaxy (MBE), photoluminescence (PL), quantum dot molecules (QDMs), selective etching.

A sharp contrast of the density and size of Ga metal droplets (MDs) on strip patterned GaAs (100) is demonstrated through droplet epitaxy (DE) and photolithography technique. As clearly evidenced by scanning electronic microscope (SEM) and atomic force microscope (AFM), MD density between etched (patterned) and un‐etched (un‐patterned) surfaces can be sharply different up to one order of magnitude under an identical growth condition. Etched surface exhibits much higher density and smaller diameter and height of MDs.

Due to the highly flexible nature of self‐assembly and a wide range of applications in molecular beam epitaxy, droplet epitaxy is gaining significant research interest for the fabrication of low‐dimensional semiconductor quantum‐ and nano‐structures by self‐assembly. Optoelectronic device applications such as solar cells using GaAs quantum rings, inter‐sublevel infrared photodetectors and lasers have been demonstrated through droplet epitaxy. Thus, the control of density and size of metal droplets (MDs) on a patterned GaAs(100) surface becomes an essential step for further development. Ming‐Yu Li et al. (pp. ) present an attempt to demonstrate a sharp contrast in size and density of Ga MDs on patterned GaAs(100) through conventional photolithography. The etched surface exhibits a much higher density and smaller diameter and height of MDs. As clearly evidenced by SEM and AFM, the MD density between etched (patterned) and un‐etched (un‐patterned) surfaces can be sharply different up to one order of magnitude under identical growth conditions.