Temperature Activated Dimensionality Crossover in the Nucleation of Quantum Dots by Droplet Epitaxy on GaAs(111)A Vicinal Substrates

Abstract

A temperature activated crossover between two nucleation regimes is observed in the behavior of Ga droplet nucleation on vicinal GaAs(111)A substrates with a miscut of 2° towards $$(\bar{1}\bar{1}2)$$ ( 1 ¯ 1 ¯ 2 ) . At low temperature (<400 °C) the droplet density dependence on temperature and flux is compatible with droplet nucleation by two-dimensional diffusion. Increasing the temperature, a different regime is observed, whose scaling behavior is compatible with a reduction of the dimensionality of the nucleation regime from two to one dimension. We attribute such behavior to a presence of finite width terraces and a sizeable Ehrlich-Schwöbel barrier at the terrace edge, which hinders adatom diffusion in the direction perpendicular to the steps.

Nucleation of Ga droplets self-assembly on GaAs(111)A substrates

“…The activation energy, calculated from the temperature dependence of the island density, is . This value is in between the ones, which we calculated for the Ga droplet nucleation on vicinal GaAs(111)A 21 . It is assumed that the the Ga droplet nucleation on singular GaAs(111)A is characterized by both types of diffusion (one- and two-dimensional).…”

“…Additionally, the characteristic parameters of the nucleation process such as the activation energy and the size of stable cluster i (the number of atoms that are the part of the largest unstable cluster 17 , 18 ) can be obtained from the capture zone distribution (CZD) approach 21 , 28 , 29 . The capture zone (CZ) is the area from which, on average, the adatom constituting the island are collected.…”

“…As shown in Refs. 19 – 21 , the density of DE QDs, when crystallized at the same temperature used for the deposition of the metal droplets, mirrors that of droplets, thus making possible to access the density dependence of Ga droplets on the deposition parameters through the measurement of the island density. The crystallized surface morphology is more stable on time and avoids the strong oxidation effects which would hinder the reproducibility of the atomic force microscope (AFM) measurements.…”

Atomic-Scale Characterization of Droplet Epitaxy Quantum Dots

“…The elongation of QD shape is a natural consequence of the SK growth technique. Various techniques can be used to obtain QDs with small FSS such as, growing QDs on (111) surfaces in which the underlying C crystal symmetry assists in obtaining uniform QDs [ 107 , 108 , 109 , 110 , 111 ]. Fabrication of QDs in locally etched pits is another technique to reduce anisotropy in QDs size and shape [ 112 ].…”

Reentrant Behavior of the Density vs. Temperature of Indium Islands on GaAs(111)A

“…These critical requirements can be mitigated using a vicinal (111) surface, in which the growth conditions (high growth rate and low V/III ratio) are similar to those for a GaAs(001) surface thanks to the presence of preferential nucleation sites at the step edges. Ga droplet nucleation on the vicinal GaAs(111)A substrate was already studied and a temperature activated dimensionality crossover at ~400 C in the nucleation of QDs was observed [ 21 ], which has the effect of decreasing the droplet density activation energy at high temperatures.…”