Fabry-Perot (FP) lasers with a cavity length shorten down to 50 mu m were investigated. One or two laser mirrors were formed by focused ion beam etching. InGaAs quantum dots of high density were used as the laser active region. The lasers operate in a pulsed regime up to at least 105 degrees S. A comparison with lasers formed by the facet cleaving method (minimum length is 100 mu m) reveals the similarity of the emission wavelength and the threshold current depending on the cavity length. This allows us to conclude that the etched facets do not significantly affect the non-radiative recombination rate and provide a reflection coefficient close to that of the cleaved facet. The maximum modal gain was estimated to be not less than 240 cm-1. No evidence of the excited-state training, and similar technologies, are reserved.

This paper proposes a new approach to nanoscale patterning of GaAs substrates that allows formation of subcritical (below the Stranski-Krastanov critical thickness) low-density quantum dots. We demonstrate that the removal of the GaAs native oxide under molecular arsenic flux stimulates the formation of nanosized holes on the substrate surface. Geometric characteristics of these holes (diameter, depth and shape) can be controlled by the variation of the oxide thickness and the parameters of the oxide removal procedure. Importantly, the surface density of resulting holes shows a weak dependence on the listed parameters and remains around 1 x 109 cm-2. We show that the arsenic flux influences the processes of hole formation during the GaAs native oxide removal mainly by the modulation of the substrate thermal decomposition. We experimentally demonstrate the possibility of using GaAs substrates patterned in this way as templates for obtaining subcritical InAs quantum dot arrays with low density. We observe complete suppression of the wetting layer formation on such templates and a pronounced red shift of the emission wavelength of quantum dots grown on them (up to 1080 nm). Our results suggest that further optimization of the proposed approaches will make it possible to form low-density quantum dots emitting in the O- and C-bands.

In this work, we studied the influence of combined processing of SiO2/Si(001) substrates using focused ion beams (FIB) and wet chemical etching on the possibility of forming pyramidal cavities and their geometric parameters. It has been shown that etching FIB-modified samples only in KOH leads to the formation of pyramidal cavities covered with a shell, possibly made of porous silicon layer. We have shown that the use of an isotropic etchant before anisotropic etching allows to remove a porous silicon layer. An increase in the implantation dose led not only to an increase in the depth of the cavities, but also to an increase in the undercut of the oxide layer.

In this paper we present the results of experimental studies on the selective formation of GaAs nanowire arrays on the Si(111) substrate surface and the control of their properties. It has been shown that pre-treatment of the Si(111) surface with a native oxide layer by a focused Ga-ion beam with further low-temperature annealing and high-temperature growth allows the formation of selective GaAs nanowire arrays with a different set of parameters that can be controlled by changing the dose of ion-beam treatment. We also demonstrated the possibility of obtaining arrays with a yield of vertically oriented nanowires at the level of almost 100% and very high density (up to 8 mu m(-2)). At the same time outside the modified areas, the formation of nanowires was almost completely suppressed. Moreover, based on Raman spectroscopy study we have found that our approach allows to obtain nanowire arrays with clear zinc-blende crystal phase in wide range of nanostructure sizes.

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.

The results of a study of the optical properties of self-assembled InAs/GaAs (001) quantum dots (QDs) overgrown under different arsenic pressures, obtained using photoluminescence (PL) and PL excitation spectroscopy, are presented. If the arsenic pressure during overgrowth is low (2.5.10-6 Pa), a series of pronounced QD-related peaks is observed in the 77-K PL spectrum over a 200-meV broad spectral interval with the brightest one located at 1.37 eV. With increasing arsenic pressure, the PL spectrum becomes smoother and is red-shifted to 1.16 eV at 1.10-5 Pa and to 1.26 eV at 3.10-5 Pa. We explain this behavior in terms of enhanced QD decomposition, the mechanism of which is strongly dependent on the arsenic deficiency or excess during the overgrowth process, determined by the arsenic pressure. Supported by the analysis of the wetting layer luminescence, we also conclude that the total indium content in the QD layer decreases with decreasing arsenic pressure during the overgrowth. This study reveals an essential role of the arsenic pressure in the overgrowth of InAs QDs.

In this papaer, the emission characteristics of InAs/InGaAs quantum dot (QD) microdisk lasers, of different cavity diameters, with a top split electrical contact formed using the focused ion beam technique are investigated. The dependences of the threshold currents of two-state lasing (i.e. currents corresponding to the start of the ground- and excited-state lasing) for microdisks of 24 and 28 mu m diameters on the electrical contact area are presented. The contact area was found to influence the threshold currents of two-state lasing in microdisks. It is shown that a decrease in the area of the injected electrical contact leads to a decrease in the current corresponding to the start of the excited-state lasing, while the ground-state (GS) lasing threshold remains virtually unchanged. The temperature evolution of the threshold currents for two-state lasing was also studied in microdisks with different electrical contact areas. We demonstrate that the use of contacts of different areas is a method of controlling the threshold currents of two-state lasing and can be used in engineering of QD lasers intended, for example, for multi-level signal transmission with wavelength multiplexing by switching from the GS to excited-state lasing.

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).

We reveal a novel phenomenon observed after self-catalytic growth of GaAs nanowires (NWs) on Si(111) substrates treated with a Ga focused ion beam (FIB). Depending on the ion dose, NW arrays with various geometrical parameters can be obtained. A minor treatment of the substrate enables a slight increase in the surface density of NWs relative to an unmodified substrate area. As the ion dose is increased up to ∼0.1 pC μ m −2 , the growth of GaAs NWs and nanocrystals is suppressed. However, a further increase in the ion dose stimulates the crystal growth leading to the formation of extremely thin NWs (39 ± 5 nm) with a remarkably high surface density of up to 15 μ m −2 . Resting upon an analysis of the surface structure before and after stages of ion-beam treatment, ultra-high vacuum annealing and NW growth, we propose a mechanism underlying the phenomenon observed. We assume that the chemical interaction between embedded Ga ions and a native Si oxide layer leads either to the enhancement of the passivation properties of the oxide layer within FIB-modified areas (at low and middle ion doses), or to the etching of the passivating oxide layer by excess Ga atoms, resulting in the formation of pores (at high ion doses). Due to this behavior, local fabrication of GaAs NW arrays with a diverse range of characteristics can be implemented on the same substrate. This approach opens a new way for self-catalytic growth of GaAs NWs.

In this paper, for the first time, we report a strong effect of the arsenic pressure used for the high-rate GaAs capping of self-assembled InAs quantum dots on their optical properties. A 140 nm red shift of the photoluminescence peak position is observed when the overgrowth arsenic pressure increases threefold. We explain this behavior in terms of different intensities of quantum dot decomposition, which occurs during the overgrowth under different conditions. When the arsenic pressure is sufficiently high, a GaAs capping layer is formed by deposited species with a low impact on initial quantum dots. At a low arsenic pressure, arsenic deficiency leads to the intensive intermixing caused both by the enhanced Ga/In atom exchange and by the consumption of arsenic atoms belonging to quantum dots for the GaAs capping layer formation. As a result of the overgrowth, quantum dots are divided into families with a large (high pressure) and a small (low pressure) average size, yielding long-wave (1.23 µm) and short-wave (1.09 µm) photoluminescence peaks, respectively. Thus, a significant influence of the overgrowth arsenic pressure on the characteristics of InAs quantum dots is evidenced in this study.

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.

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.

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 a complex experimental and theoretical study of the droplet epitaxial growth of In/GaAs(001) nanostructures on patterned surfaces. We observe that holes formed after GaAs overgrowth of surfaces treated with a focused ion beam are the preferred centers for the nucleation of In droplets at any temperature in a range from 250 degrees C to 350 degrees C. Good selectivity and localization of droplets are achieved along a square perimeter of holes located at a distance from 0.5 to 4.2 mu m apart. However, lower temperatures are required to provide filling of more holes and formation of an ordered array of droplet pairs. Using kinetic Monte Carlo simulations, we demonstrate growth conditions which allow filling of all holes located at variable distances in a range from 20 to 340 nm and avoiding unnecessary nucleation beyond the holes.

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.