Inthis work, it was found that in addition to the strong dose dependence of the nanowire parameters grown within the ion beam treatment area, the annealing temperature also has a significant effect. It is shown that an increase of the annealing temperature from 600 to $750^{\circ} \mathrm{C}$ leads, on the one hand, to an increase of the nanowire density up to $\sim 40 \mu \mathrm{m}^{-2}$ at the maximum dose value. On the other hand, this leads to an increase in the proportion of vertically oriented nanowires up to 100%.

We study the optical properties of InAs/GaAs(001) quantum dots (QDs) overgrown under different V/III flux ratios using photoluminescence (PL) and excitation spectroscopy. When the V/III flux ratio is low, a series of pronounced QD-related peaks is observed in the $77-\mathrm{K}$ PL spectrum over a $200-\mathrm{meV}$ broad spectral interval with the brightest one located at 1.37 eV. With increasing V/III flux ratio, the PL spectrum is red-shifted (to 1.16 eV) and then blue-shifted again (to 1.26 eV), while becoming smoother. We explain this behavior in terms of enhanced QD decomposition, the mechanism of which is different in cases of deficiency and excess of arsenic during the overgrowth.

We presents the results of experimental studies of the formation processes and optical properties of ordered arrays of Ga(Al)As nanostructures on $\mathrm{GaAs}(\mathbf{0 0 1})$ substrates with regular arrays of pyramidal-shaped holes. The possibility AIGaAs solid solution on a structured surface decomposes with the formation of low-dimensional structures enriched by the Ga component is demonstrated. We have also shown that the emission wavelength $(740 \mathbf{n m})$ of site-controlled Ga(Al) As nanostructures is practically independent of the patterned surface morphology, while the emission intensity is determined by the effective volume of nanostructures.

In this paper, we study the effect of annealing of GaAs(111) substrates under various conditions on the morphological characteristics of nanoholes formed by focused ion beams. In the absence of annealing and when annealing in the absence of the arsenic flux, the depth and lateral size of nanoholes increase with the number of ion beam passes. In the case of annealing of the substrates in the arsenic flux, the dependences of the hole depth and lateral size on the number of beam passes is non-monotonic, which is attributed to the competition of the processes of surface etching by gallium droplets during thermal oxide removal and droplet crystallization in the arsenic flux. We demonstrate technological conditions enabling formation of highly symmetric nanoholes in the form of triangular pyramids.

In this work we study the optical properties of InAs quantum dots grown on the GaAs(001) nanostructured surfaces at sub-critical thickness of deposition. For substrate nanostructuring we used technique based on two-stage thermal desorption of native GaAs oxide under molecular arsenic flux. The results of experimental studies showed the possibility of quantum dots formation on structured surfaces at equivalent deposition thicknesses in the range of 0.5-1.5 ML. In this case, quantum dots are formed predominantly in nanoholes on the surface and are high inhomogeneous in size. At the same time measurements by photoluminescence spectroscopy showed broad (900-1100 nm) emission spectrum for quantum dot only for sample with 1.5 ML of InAs. We hypothesize that at smaller thicknesses, the formed quantum dots become smaller than the minimum acceptable sizes due to segregation effects during overgrowth. The use of a structured surface also makes it possible to suppress the wetting layer formation - in the photoluminescence spectra there are only lines of platelets, apparently formed on morphological inhomogeneities outside the holes.

Experimental studies of the effect of dose and accelerating voltage during ion beam treatment of the Si(111) surface on the substrate structure and growth processes of GaAs nanowires have been carried out. For this purpose, arrays of areas were created on the Si(111) surface by ion beam treatment using an all-over template with variation of accelerating voltage in the range of 10-30 kV and dose in the range of 0.01-10.4 pC/mu m2. Based on the results of the modified surface study after GaAs nanowire growth, the dependences of the main nano-wire characteristics (density, length and diameter) on the ion beam dose were obtained. It is shown that the main influence on the formed nanowire characteristics is exerted by the dose of embedded Ga-ions. By changing the value of this ion beam parameter together with the high-temperature annealing, the chemical composition and morphology of the surface silicon oxide layer can be locally controlled, thereby predetermining the parameters of the growing nanowire array. In this case, the accelerating voltage, and, hence, the distribution of ions in the near-surface layer, is of secondary importance during all-over template processing. This is confirmed by the formation of identical nanowire arrays at different accelerating voltages since the growth of nanowires occurs under the same conditions on the Si surface after the annealing stage (as confirmed by Raman spectroscopy results).

In this work we present the results of experimental studies of the InAs/GaAs quantum dot formation in subcritical growth modes on nanopatterned substrates. For this purpose, we used two ways for surface patterning: local droplet etching and modified oxide desorption technique. We have experimentally shown that both methods allow in situ formation of nanosized pits (or nanoholes) on the surface, but their shape and density is quite different. We also have shown that the using of growing surface nanopatterning allows both to obtain self -assembled nanostructures (including QD) at subcritical deposition thicknesses and to localize its formation in nanoholes with high selectivity and suppressing a wetting layer formation. In addition, our results have also shown that the nanohole character on a structured surface (shape, size, density) has a key effect on both the processes of nanostructure nucleation and growth and their structural and optical properties, which should also be taken into account when developing methods for creating heterostructures with regular arrays of quantum dots.

In this paper we presents the results of studying the molecular arsenic flux effect on the processes of native oxide thermal desorption and the resulting surface morphology of GaAs(001) substrates. We have shown that the exposure of GaAs under As flux at the stage of oxide removal significantly modulates the decomposition of native oxide and its chemical interaction with substrate materials. Based on the obtained experimental results and analysis of possible chemical reaction in this system we have shown that in the presence of arsenic molecules on the surface, free gallium atoms bind with it and no longer participate in the decomposition of native oxide components. This leads to additional decomposition of the substrate materials as a result of its etching. As a result, nanoholes of lower density, but larger in size, are formed on the surface. We have also shown that a decrease in the oxide thickness leads to a decrease in the density and dimensions of the nanoholes.

This paper presents the results of the experimental studies of InAs quantum dot overgrowth by a low-temperature GaAs layer at different arsenic vapor pressures. It is revealed that a threefold decrease in the arsenic pressure at a fixed deposition rate of the capping layer leads to a change in the shape of the photoluminescence spectrum of quantum dots with one maximum at the level of 1.19 eV to the shape of the spectrum with two low-energy contributions at the levels of 1.08 and 1.15 eV. Based on the analysis of the power dependences of the photoluminescence spectra, it is found that the low-energy contributions of the photoluminescence of quantum dots overgrown at a low arsenic pressure correspond to the ground-state emission two groups of quantum dots with different average sizes formed during mass transfer in the “quantum dot – wetting layer – matrix” system.

This paper presents the results of experimental studies of the effect of the Ga ion dose during ion-beam treatment of the Si(111) surface using the focused ion beam technique on the GaAs nanowires epitaxial growth processes. A significant difference is revealed between the parameters of nanowire arrays formed on modified and unmodified areas of the Si substrate in this way. It is shown that changing the Ga ions dose from 0.052 to 10.4 pC/μm^2 during ion-beam treatment makes it possible to form GaAs nanowires arrays with a different set of parameters in a single technological cycle with a high degree of localization. The regularities of the influence of the dose of Ga ions during surface modification on the key characteristics of GaAs nanowires (density, diameter, length, and orientation with respect to the substrate surface) are experimentally established.

lakhina@sfedu.ru Abstract. GaAs nanostructures are promising candidates for use in future nanoelectronics and quantum photonics. However, technology of their controllable fabrication with precisely predefined size, shape and surface density still requires further improvement. In this paper, we reveal a possibility to reduce a size of gallium droplets using exposure to the arsenic flux of ul-tra-low values. The control of size and shape of droplets is implemented independently of their surface density that enables formation of low-density arrays of small-sized quantum dots. Based on droplet arrays with trimodal size distribution, we demonstrate that droplets with larger sizes are less influenced by the low arsenic flux whereas smaller droplets may reduce in volume or decay completely resulting in the formation of nanoholes. The technique under consideration can be used for the fabrication of single quantum dot devices with specified characteristics.

The paper presents the results of experimental studies of GaAs nanowire growth on Si(111) substrate with Ga focused ion beam modified areas with different treatment doses. We observed a significant difference between the parameters of nanowires arrays formed on modified and unmodified areas. It is shown that changing the dose of Ga ions from 52 fC/ mu m2 to 1x104 fC/mu m2 allows to form nanowire arrays with a different set of parameters in a single technological cycle with a high selectivity. The possibility of regulating of the NW length in the range of 1-6 mu m, the density in the range of 0-7.8 mu m-2, the diameter in the range of 28-95 nm and the normally oriented NWs in the range of 5-70 % by focused ion beam have been experimentally demonstrated. The change of modes and mechanisms of the catalytic centers formation and the initial stage of GaAs NWs growth were revealed.

In this paper, we demonstrate a novel technique enabling fabrication of small sized InAs/GaAs quantum dots with a very low surface density during droplet epitaxy. In contrast to the traditional two-stage approach, we introduce an additional stage of exposure to the ultra-low arsenic flux which enables partial diffusion decay of droplets with a large initial size. While exposure of droplets to large arsenic fluxes leads to their transformation into rings, disks and holes, exposure to the ultra-low flux makes it possible to reduce the volume of droplets maintaining their initial surface density. At the following stages of crystallization and annealing, In droplets are converted into InAs quantum dots with an average diameter below 30 nm and a surface density below 108 cm-2. The standard deviation of quantum dot diameters is found to be less than 5%. Furthermore, we demonstrate that the growth procedure is well-reproducible, which makes it a promising method of quantum dot fabrication for advanced nanophotonic devices.

In this work, we study of the effect of focused ion beam (FIB) and pre-growth treatment based on local droplet etching (LDE) techniques combination on the regular nano hole array formation on GaAs (001) surface, which can act as template for selective quantum dot formation in future. The results of the influence of the regimes of method combination on the nanohole shape and size are presented. Based on the analysis of Raman spectra, we have shown that the use of LDE-based technique makes it possible to almost restore the crystal structure of FIB-modified regions completely. The possibility of obtaining highly symmetrical, faceted by {101} and {011} planes nanoholes of various diameters and depths in selected surface points in one technological cycle is shown.

In this paper, we present the results of studying the influence of arsenic pressure in the range of ultra-low values (10^-7-10^-6 Pa) on the processes of modification of In/GaAs(001) droplets with various initial sizes obtained by droplet epitaxy. We experimentally demonstrate that exposure of droplets to the ultralow arsenic flux makes it possible to reduce the droplet size to subcritical sizes while maintaining the initially specified surface density. The exposure of droplet nanostructures in the arsenic flux can be accompanied only by a decrease in their size, which is more typical for droplets obtained at large amounts of indium deposited material. For droplets with a smaller initial size, the formation of rings along the perimeter of the initial droplets and holes inside the rings is typical along with the droplet reduction. We also reveal that the dependence of the relative volume of droplets subjected to diffusion decay in the arsenic flux becomes more significant with a decrease in their initial size.

In this paper, we present a study of the effect of the silicon substrate modification by focused ion beams on subsequent growth of GaAs layers by molecular beam epitaxy. We demonstrate that when samples exposed to the ion irradiation at various accelerating voltages and ion beam passes are annealed in the absence of the arsenic flux, an increase in the depth of the modified Si substrate areas occurs. At the same time, crystallization of gallium accumulations during annealing in the arsenic flux leads to the filling of holes formed during the ion bombardment. We reveal that the growth of GaAs on substrates with areas modified at an accelerating voltage of 30 kV and subjected to subsequent annealing in the arsenic flux at a temperature of 600 o C is accompanied by the formation of nanowires, the density of which increases within areas with a large number of ion beam passes. The results of the conducted research can be used for the development of technological approaches to the formation of GaAs epitaxial layers on Si substrates. Keywords: molecular beam epitaxy, monolithic integration, gallium arsenide, silicon, focused ion beams.

In this paper, we present the results of studying the influence of arsenic pressure in the range of ultra-low values (10 -7 -10 -6 Pa) on the processes of modification of In/GaAs(001) droplets with various initial sizes obtained by droplet epitaxy. We experimentally demonstrate that exposure of droplets to the ultralow arsenic flux makes it possible to reduce the droplet size to subcritical sizes while maintaining the initially specified surface density. The exposure of droplet nanostructures in the arsenic flux can be accompanied only by a decrease in their size, which is more typical for droplets obtained at large amounts of indium deposited material. For droplets with a smaller initial size, the formation of rings along the perimeter of the initial droplets and holes inside the rings is typical along with the droplet reduction. We also reveal that the dependence of the relative volume of droplets subjected to diffusion decay in the arsenic flux becomes more significant with a decrease in their initial size. Keywords: droplet epitaxy, nanostructures, In(As)/GaAs, arsenic flux.

This paper presents the results of experimental studies of the effect of the Ga ion dose during ion-beam treatment of the Si(111) surface using the focused ion beam technique on the Ga + nanowires epitaxial growth processes. A significant difference is revealed between the parameters of nanowire arrays formed on modified and unmodified areas of the Si substrate in this way. It is shown that changing the Ga ions dose from 0.052 to 10.4 pC/μm 2 during ion-beam treatment makes it possible to form GaAs nanowires arrays with a different set of parameters in a single technological cycle with a high degree of localization. The regularities of the influence of the dose of Ga ions during surface modification on the key characteristics of GaAs nanowires (density, diameter, length, and orientation with respect to the substrate surface) are experimentally established. Keywords: Focused ion beam, nanowires, GaAs, molecular beam epitaxy.

In this paper, we present a study of the effect of the silicon substrate modification by focused ion beams on subsequent growth of GaAs layers by molecular beam epitaxy. We demonstrate that when samples exposed to the ion irradiation at various accelerating voltages and ion beam passes are annealed in the absence of the arsenic flux, an increase in the depth of the modified Si substrate areas occurs. At the same time, crystallization of gallium accumulations during annealing in the arsenic flux leads to the filling of holes formed during the ion bombardment. We reveal that the growth of GaAs on substrates with areas modified at an accelerating voltage of 30 kV and subjected to subsequent annealing in the arsenic flux at a temperature of 600 °C is accompanied by the formation of nanowires, the density of which increases within areas with a large number of ion beam passes. The results of the conducted research can be used for the development of technological approaches to the formation of GaAs epitaxial layers on Si substrates.

In this paper, we present the results of an experimental study of the influence of the ultra-low arsenic flux on the parameters of In nanodroplets obtained by droplet epitaxy on the GaAs substrate. We demonstrate that the arsenic flux can be used to alter the size of droplets without changing their surface density. An increase in the arsenic flux leads to a reduction of the nanostructure size or their complete decay. However, we demonstrate that certain growth conditions allow providing saturation of the size of nanostructures (∼30 nm) which ensures good reproducibility of the process. The mechanism of ring and hole formation at various arsenic fluxes is also discussed.