Dynamics of self-assembled droplet etching

Abstract

We study the self-assembled local droplet etching of nanoholes in AlGaAs surfaces with Ga droplets. The data establish an unexpected delay of both the hole drilling process as well as the removal of the liquid material after etching. Furthermore, coarsening by Ostwald ripening is found to reduce the droplet density before drilling. Basing on these findings, we propose a growth, coarsening, drilling, and removal mechanism for the droplet etching process.

Holed nanostructures formed by aluminum droplets on a GaAs substrate

“…1(a), there are 11 large holed nanostructures of similar size (100 nm ± 10 nm) together with nearly a hundred small holed nanostructures of various size (40 nm ± 20 nm). The sizes of the Al holed nanostructures vary more widely than those of Ga holed nanostructures observed in previous work [18][19][20][21]. This suggests that the deposited Al atoms are more chemically reactive and less mobile than Ga atoms deposited on a GaAs substrate.…”

“…The holed nanostructures, first demonstrated by Wang et al [21], are particularly promising candidates for the formation of uniform and low-density quantum rings [22][23][24]. However, all the previously published work has involved the formation of nanostructures from gallium (Ga) or indium (In) droplets [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], and there has been no report of aluminum (Al) droplets on GaAs substrates, although there have been a few of papers involving Al droplets [11,25]. Investigation of the nanostructures formed from Al droplets will not only enrich our knowledge of group Ⅲ droplet epitaxy and facilitate an understanding of provide a solid understanding of such a simple and novel molecular beam epitaxy (MBE) growth process [26].…”

“…A significant advantage of droplet epitaxy growth is its flexibility in that it is applicable to both latticemismatched and lattice-matched systems. Since the initial work by Koguchi et al [10], various dot-like [11][12][13], ring-like [14][15][16][17], and hole-like nanostructures [18][19][20] have been observed on Ⅲ-Ⅴ semiconductors.…”

Air-gap heterostructures

“…During this annealing time, the nanohole etching took place. 11 Figure 2 shows a typical atomic force microscopy ͑AFM͒ image of a GaAs surface with Ga-droplet etched nanoholes. With the above process conditions, the average hole depth is of about 10 nm, the diameter of 50 nm, and the density of around 3 ϫ 10 8 cm −2 .…”

“…[1][2][3][4][5][6][7] At high process temperatures and minimized As pressure, the droplets locally remove the substrate material which results in the self-assembled formation of nanoholes on the substrate surface. [8][9][10][11][12][13] Recently, the fabrication of strain-free GaAs quantum dots has been demonstrated by filling of such nanoholes in AlGaAs and AlAs surfaces. [14][15][16] In the present letter, in situ LDE and nanohole filling was combined with ex situ selective etching to form air-gap heterostructures.…”