Quantum dot self-assembly on GaAs(110) planar layers and nanowire facets driven by a surfactant-induced morphological instability

Three-dimensional (3D) islands that act as quantum dots (QDs) are typically synthesized by a self-assembly process known as Stranski−Krastanov (SK) growth, one of the three fundamental modes of epitaxy. In general, the preferred growth mode of a system is determined by energetic considerations, which are fixed by the choice of adsorbate and substrate. To some extent these thermodynamic constraints can be overcome kinetically, either by adjusting deposition conditions or by changing the surface chemistry using surface segregating elements, allowing 3D island formation to be kinetically suppressed in favor of two-dimensional (2D) layer-by-layer growth. However, control over the energetically preferred growth mode, as well as inducing 3D island formation when 2D growth is favored, has remained elusive. And as a result, QD synthesis has been restricted in terms of materials and substrate orientations

Figure 1. (a)–(b) Atomic force microscopy surface topographs after deposition of 2.1 monolayers of InAs on GaAs(110) (a) without and (b) with subsequent exposure of the layer to a Bi flux of 0.4 monolayers/s. The Bi exposure induces a morphological phase transition in the atomically smooth 2D InAs layer, resulting in the formation of InAs 3D islands. The scale bar and crystallographic directions shown in (a) also apply to (b). (c)(d) Scanning electron micrographs of dispersed nanowires of about 60 nm diameter after depositing InAs under a Bi flux. The nominal InAs thicknesses are (a) 1.4 monolayers and (b) 3.5 monolayers. (c) After 1.4 monolayers of InAs, 3D objects appear on the nanowire sidewalls. (d) At 3.5 monolayers InAs deposition, zig-zag nanorings completely encircling the nanowire core are observed. (e) Photoluminescence spectra taken at 9 K from as-grown capped nanowire samples containing 1.4 monolayers of InAs grown with and without the presence of a Bi flux. Scans from two regions of the sample grown with Bi show a series of narrow transitions in the 1.31.4 eV energy range, and the wetting layer emission is blue-shifted compared to the sample grown without Bi. The inset shows transitions with widths of about 120 eV (resolution limited) from the sample grown with Bi.

Here we show that surfactants can provoke morphological phase transitions in strained layers, inducing the formation of 3D islands “on-demand”. We explore Bi as a surfactant in the growth of InAs on GaAs(110) by molecular beam epitaxy, and find that the presence of surface Bi induces SK growth of 3D islands, while growth without Bi always favors 2D layer formation. Density functional theory calculations reveal that surface Bi reduces the energetic cost of 3D island formation by altering the surface energy of the GaAs and InAs surfaces. We exploit this effect to induce the formation of InAs 3D nanostructures directly on the {110} sidewalls of GaAs nanowires, realizing a series of novel nanostructures ranging from InAs 3D islands to zig-zag shaped nanorings. The small 3D islands behave as optically active QDs, demonstrating their perspective for quantum optics embedded in GaAs nanowires. This work illustrates how modifying surface energies with surfactants can allow for unprecedented control over nanostructure self-assembly.

2 Author R. B. Lewis , P. Corfdir , J. Herranz , H. Küpers , U. Jahn , O. Brandt , L. Geelhaar

Self-assembly of InAs nanostructures on the sidewalls of GaAs nanowires directed by a Bi surfactant

Source Nano Lett. , 17 , 4255 ( 2017 )
DOI : 10.1021/acs.nanolett.7b01185 | Download arXiv: 1704.08014 | 2910 Cite : Bibtex RIS
R. B. Lewis, P. Corfdir, J. Herranz, H. Küpers, U. Jahn, O. Brandt, and L. Geelhaar

1 Author R. B. Lewis , P. Corfdir , H. Li , J. Herranz , C. Pfüller , O. Brandt , L. Geelhaar

Quantum dot self-assembly driven by a surfactant-induced morphological instability

Source Phys. Rev. Lett. , 119 , 086101 ( 2017 )
DOI : 10.1103/PhysRevLett.119.086101 | Download: PDF | 2903 Cite : Bibtex RIS
R. B. Lewis, P. Corfdir, H. Li, J. Herranz, C. Pfüller, O. Brandt, and L. Geelhaar