We present a new method for the deposition of colloidal Au nanoparticles on the surface of silicon substrates based on short-time Ar plasma treatment without the use of any polymeric layers. The elaborated method is compatible with molecular beam epitaxy, which allowed us to carry out the detailed study of GaAs nanowire synthesis on Si(111) substrates using colloidal Au nanoparticles as seeds for their growth. The results obtained elucidated the causes of the difference between the initial nanoparticle sizes and the diameters of the grown nanowires.

Heterostructures with multiple strongly coupled quantum wells, such as super-multiperiod (SMP) superlattices (SLs), are promising semiconductor devices, which may contain hundreds or even thousands of layers with 100 or more periods synthesized by molecular beam epitaxy (MBE) to high structural perfection. The proposed characterization method employs matched application of high-resolution x-ray diffractometry (XRD), reflectometry (XRR), and, for the first time, the deep XRR (DXRR) allows the study of SMP structures, as well as high-accuracy determination of the thicknesses of layers, roughness/diffuseness of boundaries using the rigorous scattering theory, and composition of solid solutions. Combining these methods with scanning transmission electron microscopy (STEM) enables characterization of SMP SLs and independent determination of these same parameters. The differences between the expected and obtained layer thicknesses by XRD and XRR were 1%-3% for AlGaAs/GaAs structures. The samples were characterized by sharp interfaces with the root-mean-square width of the transition layers of the order of a few Å, which is consistent with the XRR/DXRR and STEM analysis. Based on the data obtained for the thicknesses of layers, the composition of Al 0.3 Ga 0.7 As has been accurately determined by the x-ray methods. These results may be considered as the first step in the analysis of MBE-grown SMP structures with a number of periods up to 1000.

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The electronic properties of semiconductor AIIIBV nanowires (NWs) due to their high surface/volume ratio can be effectively controlled by NW strain and surface electronic states. We study the effect of applied tension on the conductivity of wurtzite In x Ga 1−x As (x ∼ 0.8) NWs. Experimentally, conductive atomic force microscopy is used to measure the I−V curves of vertically standing NWs covered by native oxide. To apply tension, the microscope probe touching the NW side is shifted laterally to produce a tensile strain in the NW. The NW strain significantly increases the forward current in the measured I−V curves. When the strain reaches 4%, the I−V curve becomes almost linear, and the forward current increases by 3 orders of magnitude. In the latter case, the tensile strain is supposed to shift the conduction band minima below the Fermi level, whose position, in turn, is fixed by surface states. Consequently, the surface conductivity channel appears. The observed effects confirm that the excess surface arsenic is responsible for the Fermi level pinning at oxidized surfaces of III-As NWs.

The realization of GaAs nanowire (NW) high-performance quantum devices operated at room temperatures requires that their diameters have to be less than 10 nm. It is shown, that the GaAs NWs with sub 10 nanometers diameters can be fabricated using the thermal decomposition technique. It is demonstrated, that depending on annealing conditions, the NW lengths, as well as shapes, can be modified significantly. The GaAs NWs with bottle-like and diameter-modulated shapes can be obtained. At the first stage of the thermal annealing in the presence of As flux, an increase in NW length was found.

Control of directionality of emissions is an important task for the realization of novel nanophotonic devices based on nanowires. Most of the existing approaches providing high directionality of the light emitted from nanowires are based on the utilization of the tapered shape of nanowires, serving as nanoantenna coupling with the light waveguided in nanowire and the directional output beam. Here we report the beaming of the emitted light with wavelength near 800 nm by naturally formed core-shell AlGaAs NW with multiply GaAs quantum dots (QDs) diameter 30 nm and height 10 nm, while the diameter of NW 130 nm, what does not support efficient emission into waveguided modes, including the mode HE11. Experimental measurements show that intensity of emission for directions in the vicinity of the axis of NW is about two orders of magnitude higher than for perpendicular directions. The developed theoretical approach allowed us to calculate the probability of spontaneous emission for various directions and into waveguided modes and showed that highly directional radiation can be provided by the intrinsic emission properties of cylindrical NW. Our results suggest that for the small diameter of NW, directional emissions are associated with an TM0 leaky mode (when electric field oriented in axial direction) and therefore manifests in an existence of axial electric dipole transitions in quantum dots.

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