Mechanism of nucleation and critical layer formation during In/GaAs droplet epitaxy

Abstract

Fabrication of A III B V nanostructures by droplet epitaxy has many advantages over other epitaxial techniques. Although various characteristics of the growth by droplet epitaxy have been thoroughly studied for both lattice-matched and mismatched systems, little is known about physical processes hindering the formation of small size InAs/GaAs nanostructure arrays with low density and thin wetting layer. In this paper, we experimentally demonstrate that the indium droplet diameter can be reduced by decreasing the deposition time, but this reduction is limited by a critical thickness of droplet formation dependent on the substrate temperature. Using the kinetic Monte Carlo model, we propose a mechanism considering that the droplet formation begins when the system overcomes a barrier determined by the substrate attraction. As a result of physical and chemical balancing between adatom aggregation and substrate wetting, this attraction becomes weaker with increasing either temperature or deposition amount, which leads to the critical layer formation and subsequent nucleation. Using this mechanism, it is possible to provide a wide control over the nanostructure growth which is especially important at high temperatures when the processes of the island ripening are particularly intensive.

Independent Control Over Size and Surface Density of Droplet Epitaxial Nanostructures Using Ultra-Low Arsenic Fluxes

“…The GaAs surface, which is initially arsenic-stabilized, becomes metal-stabilized after the In deposition. Then, droplets formed on the surface go into a stable equilibrium state in which the material balance is settled between the wetting layer (1 ML or more [ 24 , 27 , 29 ]) and droplets on the surface. Atoms do not migrate from the wetting layer to droplets because of their attraction by arsenic atoms in the substrate.…”

“…Thereby, we carried out studies on droplets obtained after the deposition of a minimal amount of material leading to droplet formation. According to our previous work [ 27 ], a critical deposition amount for the In/GaAs system at a temperature of 300 °C is 1 ML. After exposing critical droplets formed at this deposition amount to the ultra-low arsenic flux, we found out that these droplets were very unstable and completely decayed at an arsenic pressure ratio above 2.…”

“…After the buffer layer growth, the substrate was cooled down to a deposition temperature of 300 °C with the valve fully closed. The choice of this deposition temperature was associated with the surface density of droplets observed after In deposition at this temperature (10 8 cm −2 or less) [ 24 , 27 , 48 ]. At this density, the distance between droplets is more than 1 µm, which is convenient for the separation of quantum structures.…”

“…It is commonly known that the higher the temperature used during growth by any of the techniques (Stranski–Krastanov or droplet epitaxy), the lower the surface density and the larger the average size of islands become [ 24 , 26 , 27 , 28 , 29 ]. In order to avoid the inter-dependence of the island size and surface density, various approaches have been applied, such as growth on patterned substrates [ 30 , 31 ], the use of subcritical deposition amounts [ 27 , 29 , 32 , 33 ], growth on metal-stabilized surfaces [ 34 , 35 ], etc. However, the simultaneous achievement of a low density and small size of nanostructures is still a relevant problem.…”

Resistive Switching of GaAs Oxide Nanostructures

“…After the chemical etching of ONSs, formed on the surface of GaAs epitaxial structure by the LAO method, it is possible to create profiled nanoscale structures (PNSs) as a centers for localizing quantum dots growth [35][36][37][38], nanowires [39,40], and also antilattices used in the development of the element base of quantum computers [41]. For the manufacture of such structures, it is necessary to form ONS and then PNS on the GaAs surface with specified geometric parameters.…”