Hybrid AlGaAs/GaAs/AlGaAs nanowires with a quantum dot grown by molecular beam epitaxy on silicon

Data on the growth features and physical properties of GaAs inserts embedded in AlGaAs nanowires grown on Si(111) substrates by Au-assisted molecular beam epitaxy are presented. It is shown that by varying the growth parameters it is possible to form structures like quantum dots emitting in a wide wavelength range for both active and barrier regions. The technology proposed opens up new possibilities for the integration of direct-band III–V materials on silicon.     

Indium nanowires at the silicon surface

Conductive indium nanowires up to 50 nm in width and up to 10 μm in length are fabricated on the surface of silicon by local resputtering from the probe of an atomic-force microscope. The transfer of indium from the probe of the atomic-force microscope onto the silicon surface is initiated by applying a potential between the probe and the surface as they approach each other to spacings, at which the mutual repulsive force is ~10^–7 N. The conductivity of the nanowires ranges from 7 × 10^–3 to 4 × 10^–2 Ω cm, which is several orders of magnitude lower than that in the case of the alternative technique of heat transfer.     

Electronic properties of silicon nanowires

The electronic structure and transmission coefficients of Si nanowires are calculated in a sp/sup 3/d/sup 5/s/sup */ model. The effect of wire thickness on the bandgap, conduction valley splitting, hole band splitting, effective masses, and transmission is demonstrated. Results from the sp/sup 3/d/sup 5/s/sup */ model are compared to those from a single-band effective mass model to assess the validity of the single-band effective mass model in narrow Si nanowires. The one-dimensional Brillouin zone of a Si nanowire is direct gap. The conduction band minimum can split into a quartet of energies although often two of the energies are degenerate. Conduction band valley splitting reduces the averaged mobility mass along the axis of the wire, but quantum confinement increases the transverse mass of the conduction band edge. Quantum confinement results in a large increase in the hole masses of the two highest valence bands. A single-band model performs reasonably well at calculating the effective band edges for wires as small as 1.54-nm square. A wire-substrate interface can be viewed as a heterojunction with band offsets resulting in reflection in the transmission.     

Formation of a hybrid pn junction via p-type aluminium induced crystallized polycrystalline silicon on hydrothermally grown n-type zinc oxide nanowires

p-Type silicon coated zinc oxide (ZnO) nanowire heterojunction was fabricated using a combination of aluminium induced crystallization (AIC) and hydrothermal growth. The p-type AIC Si/n-type ZnO nanowires stacked layers were extensively characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), UV–vis spectroscopy, XRD, photoluminescence emission spectroscopy and electrical measurements. Photovoltaic measurements indicate that the device is light-sensitive and maybe of potential in sensor applications.     

Cr-MIS solar cells using thin epitaxial silicon grown on poly-silicon substrates

Cr-MIS solar cells were fabricated on 18-30 µm epitaxial-Si layers grown on poly-Si substrates. Solar conversion efficiency values ranged from an average of 8.8% to 4.0% depending on choice of substrate. Nonuniformity of certain substrates led to low efficiency values. Interface state density > 5 × 10¹²/cm²-eV contributed to low Vocand high n-factor. Low minority carrier diffusion length caused Jscto drop to 60% of the optimum value. Substrates with imperfections caused an increase in dark current density by three orders of magnitude, which served to decrease photovoltaic response. The procedures given herein could lead to a low-cost solar cell for terrestrial applications.     

Properties of GaAsN nanowires grown by magnetron-sputtering deposition

The effectiveness of magnetron-sputtering deposition in an Ar-N₂ plasma-forming mixture as a technique for the fabrication of arrays of GaAs_{1 ? x} N _x nanowires (NWs) with typical diameters from 10 to 200 nm and lengths up to 3000 nm is demonstrated. Dependence of the growth character of NW on the parameters of the synthesis process, such as the size of Au droplets, deposition rate, and crystallographic orientation of the surface and the temperature of the substrate, is investigated. Analysis of the dependence of NW height on their diameter demonstrates that growth occurs predominantly by the diffusion mechanism. The nitrogen content is kept stable for growth temperatures in the range 400–500°C, being as high as 2.7%. For the substrate temperatures in the range 530–600°C, an abrupt drop in the nitrogen content in the alloy takes place. In the photoluminescence (PL) spectra of the samples obtained, a red shift of the emission band is observed, which is related to an increase in the nitrogen content. The growth-temperature dependence of the position of the luminescence band and the nitrogen content is determined. It is found that the PL intensity of samples with GaAsN NWs containing 2.7% nitrogen increases by a factor of 5–10 as compared to samples with planar layers, which is explained by the absence of structural defects in NWs.     

Isolation of silicon film grown on porous silicon layer

We have investigated a new technology for dielectric isolation of a Si film grown epitaxially on a porous silicon layer. After oxidation of the porous silicon layer, a Si on Ohcidized Porous Silicon(SOPS) structure can be obtained. It is proposed that micropores pinch off quickly in the interfacial region between the porous silicon layer and the epitaxial film. A minimum yield calculated from Rutherford backscattering spectra of the epitaxial silicon film is 5.3%, and an electron Hall mobility of 600cm²/V.s is obtained in the film with a carrier concentration of 1 x 10¹⁷ /cm³. MOSFETs were fabricated on the SOPS structure.     

Intergrowth mechanism of silicon nanowires and silver dendrites

The intergrowth mechanism of silicon nanowires and silver dendrites formed by electroless metal deposition has been investigated by scanning electron microscopy. A self-assembled localized microscopic electrochemical cell model can adequately describe the self-organized Si nanowires growth. Using these in situ prepared Si nanowire arrays as templates, a diffusion-limited aggregation process is proposed to explain the formation of the silver dendritic nanostructures.     

Electrical characteristics of nickel silicide–silicon heterojunction in suspended silicon nanowires

Electronic characteristics of silicide/silicon interface were studied in the suspended, chemically synthesized silicon nanowires (SiNWs). Step-by-step intrusion of a silicide/Si interface along the axial direction of a suspended silicon nanowire was performed by repeated thermal annealing cycles, and the current-voltage (I-V) characteristics of the annealed silicide/SiNW/silicide structure were measured at each cycle. The intruded length of the silicide was found to be directly proportional to the total annealing time, but the rate of silicidation was much smaller than previous works on similar silicide/SiNWs. A structural kink with Ni atoms diffused along the sidewall created a secondary source of silicidation, resulting in anomalous I-V characteristics. The measured I-V including this unintentional silicidation in the Si channel was explained by various combinations of Schottky barriers and resistors.     

Planar junctions in silicon on oxide grown using lateral epitaxy by seeded solidification

Current-voltage characteristics of large planar junctions fabricated in silicon on oxide have been studied. These junctions have slightly higher reverse leakage currents and slightly lower breakdown voltages than similar junctions fabricated in bulk silicon. The electrical properties of the junctions are dependent on the regrowth parameters of the silicon films. Fairly uniform junction properties are obtained over the entire sample.     

Recombination of self-trapped excitons in silicon nanocrystals grown in silicon oxide

The kinetics of photoluminescence (PL) and steady-state PL from silicon nanocrystals formed in the SiO₂ matrix by silicon ion implantation were studied experimentally for the first time in the temperature range from liquid-helium to room temperature. A dramatic increase in the photoluminescence decay time, accompanied by PL intensity quenching, is observed below 70 K. The results obtained indicate that the silicon nanocrystal PL arises from radiative recombination of excitons self-trapped at the silicon nanocrystal-SiO₂ interface.     

Diffusion doping of undoped hydrogenated amorphous silicon with tin

The solubility of tin in undoped, hydrogenated, amorphous silicon is determined by diffusion-doping films of this material with the radioactive isotope ^119m Sn. The temperature dependence of the tin solubility is described by the relation S[cm⁻³]=4×10²² exp(−0.46/kT[eV]). Fiz. Tekh. Poluprovodn. 32, 135–136 (February 1998)     

Plasmon-loss imaging of chains of crystalline-silicon nanospheres and silicon nanowires

Nanostructures in chains of crystalline-silicon nanospheres and silicon nanowires were investigated using energy-filtered transmission electron microscopy (TEM). Observation of the shape of the silicon nanospheres in the chains provided the direct evidence that the chains were formed via the surface oxidation process, which may preferentially work at the necks. The diverse nanostructures in silicon nanowires were revealed, and we found smooth-shaped wires which have periodically modulated silicon cores. Nanostructures in wire-chain transition regions were also investigated for the first time. The wire-chain transition is not a simple junction of a silicon nanowire and a chain of silicon nanospheres, but has a periodically modulated silicon core in the wire region near the transition position.     

The defect structure of grown silicon dioxide films

A structural model is proposed to explain various phenomena which occur in grown SiO2films. In this model, oxygen interstitials in ionic form are the predominant diffusing species during the growth. In neutral form they can act as acceptor states. Reduction of the oxide by hydrogen (e.g., growth in steam, heat treatment in H2containing gas) or by metal (e.g., interaction with the gate electrode in metal-oxide-semiconductor (MOS) devices) results in trivalent silicon. This defect may form a donor surface state. The migration of metal ions under the influence of an electric field can lead to an asymmetric current-voltage characteristic of a Si-SiO2-Me system. Transient and hysteresis effects as well as the asymmetric shift in the surface potential caused by biasing MOS devices at relatively high temperatures are attributed to an inhomogeneous distribution of defects in the oxide (as a result of the oxidation) and/or to the motion of metal ions originating from the gate electrode.     

Properties of silicon films grown under different pressures in a plasma-forming system

The influence of the working-gas pressure on the properties of thin silicon films synthesized by dc magnetron sputtering is investigated. Films obtained under lower pressures are characterized by lower roughness and resistivity. These features can qualitatively be explained by the longer free particle path in the deposition flux under lower pressure.     

Diffusion saturation of nondoped hydrated amorphous silicon by tin impurity

The effect of radiation defects on the field and temperature dependences of the magnetic susceptibility of single-crystal Si was studied. A nonlinear magnetic-field-dependence of the magnetic susceptibility of irradiated Si was observed. This behavior can be explained by magnetic ordering of A centers. It was concluded that clusters of these centers with a local density of the order of 10²¹ cm⁻³ exist. An explanation of the “diffusion paradox” in the formation of oxygen-containing thermal donors was proposed on the basis of micrononuniformities of the spatial distribution of thermal donors and interstitial oxygen in Si. Fiz. Tekh. Poluprovodn. 32, 292–295 (March 1998)     

Electron-microscopic imaging of single-walled carbon nanotubes grown on silicon and silicon oxide substrates

Direct imaging of single-walled carbon nanotubes (SWNTs) suspended on pillar-patterned Si or SiO2 substrates is investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The suspended nanotubes are successfully observed by direct TEM imaging and it is seen that they have either individual or bundles of SWNTs. Low energy (< or =2 keV) SEM produces high contrast images of suspended SWNTs. On the contrary, when SWNTs contact a SiO2 substrate, they are imaged using electron-beam induced current. The image brightness depends on the length of SWNTs.     

Growth oxygen-containing defects in silicon grown in a weak vertical magnetic field

Properties of silicon (M-Si) prepared by the Czochralski growth technique in a vertical magnetic field of 0.05 T applied to a melt are studied by measuring IR absorption spectra, microindentation, and selective etching. The effect of increasing the concentration of interstitial oxygen upon the thermal treatment of M-Si is found. It is shown that microhardness of M-Si is higher than that of silicon grown by the traditional Czochralski technique by ∼8%. The features in the behavior of M-Si are attributed to the formation of oxygen-containing defect-impurity complexes during the growth. Upon thermal treatment at 900°C in the hydrogen flow, these complexes decompose with the extraction of interstitial oxygen, which suppresses thermal hardening typical of the silicon single crystals grown by the traditional Czochralski technique.