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We analyzed structural and electrical properties of axial Si-Ge nanowire heterojunctions produced by the vapor-liquid-solid growth method using Au nanoclusters as catalysts. The observed nonlinear current-voltage characteristics, strong flicker noise, and damped current oscillations with frequencies of 20–30 MHz are explained using a proposed Si-Ge nanowire heterojunction energy band diagram that includes energy states associated with structural imperfections, as revealed by transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Unstrained Ge1-xSnx layers of various Sn concentration (1.5%, 3%, 6% Sn) and Ge0.97Sn0.03 layers with built-in compressive (ε=-0.5%) and tensile (ε=0.3%) strain are grown by molecular beam epitaxy and studied by electromodulation spectroscopy (i.e., contactless electroreflectance and photo-reflectance (PR)). In order to obtain unstrained GeSn layers and layers with different built-in in-plane strains, virtual InGaAs substrates of different compositions are grown prior to the deposition of GeSn layers. For unstrained Ge1-xSnx layers, the pressure coefficient for the direct band gap transition is determined from PR measurements at various hydrostatic pressures to be 12.2±0.2meV/kbar, which is very close to the pressure coefficient for the direct band gap transition in Ge (12.9 meV/kbar). This suggests that the hydrostatic deformation potentials typical of Ge can be applied to describe the pressure-induced changes in the electronic band structure of Ge1-xSnx alloys with low Sn concentrations. The same conclusion is derived for the uniaxial deformation potential, which describes the splitting between heavy-hole (HH) and light-hole (LH) bands as well as the strain-related shift of the spin-orbit (SO) split-off band. It is observed that the HH, LH, and SO related transitions shift due to compressive and tensile strain according to the Bir-Pikus theory. The dispersions of HH, LH, and SO bands are calculated for compressive and tensile strained Ge0.97Sn0.03 with the 8-band kp Hamiltonian including strain effects, and the mixing of HH and LH bands is discussed. In addition, the dispersion of the electronic band structure is calculated for unstrained Ge1-xSnx layers (3% and 6% Sn) at high hydrostatic pressure with the 8-band kp Hamiltonian, and the pressure-induced changes in the electronic band structure are discussed. [ABSTRACT FROM AUTHOR]

Detailed studies of the structural and optical properties of axial silicon-germanium nanowire heterojunctions show that despite the 4.2% lattice mismatch between Si and Ge they can be grown without a significant density of structural defects. The lattice mismatch induced strain is partially relieved due to spontaneous SiGe intermixing at the heterointerface during growth and lateral expansion of the Ge segment of the nanowire. The mismatch in Ge and Si coefficients of thermal expansion and low thermal conductivity of Si/Ge nanowire heterojunctions are proposed to be responsible for the thermally induced stress detected under intense laser radiation in photoluminescence and Raman scattering measurements. [ABSTRACT FROM AUTHOR]

The mechanical resonance of laterally grown silicon nanowires measured by an optical interferometric technique is reported. The lengths and diameters of the nanowires ranged from L=2 to 20 μm and D=39 to 400 nm, respectively. The wires showed resonant frequencies in the f0=1–12 MHz range and resonant quality factors Q at low pressure ranging from Q=5000 to Q=25 000. The dependence of resonant frequency on the ratio of diameter to length squared, D/L2, yielded a ratio of E/ρ=9400±450 m/s. Assuming a density of ρ=2330 kg/m3, this experimental result yields an experimental Young modulus of E=205±10 GPa, consistent with that of a bulk silicon. As the wires were cooled from T=270 K to T=77 K, a 0.35% increase of resonant frequency was observed. This increase of resonant frequency with cooling resulted from a change in Young’s modulus and from the thermal contraction of silicon. The quality factor did not vary significantly from P=10-4 to 102 Torr, suggesting that viscous damping does not dominate the dissipative processes in this pressure range. Although viscous damping became important above P=102 Torr, relatively high quality factors of Q=7000 were still observed at atmospheric pressure. [ABSTRACT FROM AUTHOR]

Low impedance and negligible conductivity temperature dependence are found for micron-long Ge nanowires (NWs) grown on (p+)Si substrates. In contrast, Ge NW/(n+)Si substrate samples exhibit many orders of magnitude higher impedance, an exponential dependence of conductivity on temperature, current instabilities, and negative differential photoconductivity. Our experimental results are explained by a model that considers energy-band alignment and carrier transport in abrupt Ge NW/Si substrate heterojunctions. [ABSTRACT FROM AUTHOR]

Nanoscale islands of Ti-Si were formed by chemical vapor deposition onto a Si substrate. The islands were deposited by the H2 reduction of TiCl4 either without or with a Si-containing gas added during deposition. The Ti deposition rate increases strongly with increasing deposition temperature below 690 °C, but it increases only slowly at higher temperatures. For a fixed deposition time at the lower temperatures, the number of islands after deposition changes only slowly as the amount of Ti deposited (and the deposition temperature) varies, but the number of Ti atoms in each island changes rapidly. Adding Si from the gas phase during deposition does not change the amount of Ti deposited, but it increases the height of the deposited islands above the substrate surface plane. The amount of Si-containing gas needed to form stoichiometric TiSi2 increases with decreasing deposition temperature. The island position can be controlled by depositing on a structured Si surface. [ABSTRACT FROM AUTHOR]

To study the effect of phosphorus on the evolution of Ge islands on Si(001), phosphorus-doped islands were annealed in a H[sub 2] ambient and undoped islands were annealed in a PH[sub 3]/H[sub 2] ambient. In both cases phosphorus stabilizes the island structure and reduces coarsening during annealing. The changes of island shape during annealing are consistent with phosphorus influencing the thermodynamic properties of the islands, while the slower decrease in the density of islands when phosphorus is present is consistent with phosphorus kinetically retarding surface diffusion of Ge atoms. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Hall and resistivity measurements as functions of temperature were used to study the segregation of phosphorus in atmospheric-pressure chemical-vapor deposited, ∼300-nm-thick, polycrystalline Si[sub 0.95]Ge[sub 0.5] and Si[sub 0.9]Ge[sub 0.1] thin films, implanted at 80 keV with 6 × 10[sup 13] - 5 × 10[sup 14] P/cm², and annealed for 1 h at 800°C. Hall measurements, feasible only in heavily doped films, indicated that 29% of the dopant in Si[sub 0.9]Ge[sub 0.1] and 42% of the dopant in Si[sub 0.95]Ge[sub 0.05] were electrically inactive. The loss is consistent with dopant segregation to grain boundaries. The density of grain-boundary carrier traps is 3.6 × 10[sup 12]/cm² in Si[sub 0.95]Ge[sub 0.05] and 4.4 × 10[sup 12]/cm² in Si[sub 0.9]Ge[sub 0.1], increasing sublinearly with Ge content. [ABSTRACT FROM AUTHOR]

Si nanowires grow rapidly by chemical vapor deposition on Ti-containing islands on Si surfaces when an abundant supply of Si-containing gaseous precursor is available. The density of wires is approximately the same as the density of the nucleating islands on the Si surface, although at least two different types of islands appear to correlate with very different wire growth rates. For the deposition conditions used, a minority of long, defect-free wires form, along with more numerous wires containing defects. Energy-dispersive x-ray spectroscopy shows that the Ti-containing nanoparticles remain at the tip of the growing wires. The estimated diffusion coefficient of Si in TiSi[sub 2] is consistent with the catalyzing nanoparticle remaining in the solid phase during nanowire growth. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which focused on the evolution of the shape and size distribution of germanium (Ge) islands on silicon(001) during annealing. Background information on Ge island size and shape evolution; Sample preparation, measurement and data-analysis techniques; Experimental observations and discussion; Conclusions.

Discusses the fabrication of metal-oxide-semiconductor field-effect transistors with a buried-oxide layer implanted under only the source and drain regions. Overview of a simplified transistor-fabrication process; Use of tungsten in oxygen-implant masking; Behavior of the field oxide during oxygen implantation; Findings of scanning-electron-microscope examination and observation of the field oxide.

Presents a study that analyzed the gettering of chromium and copper metal impurities to the damaged regions of silicon-on-insulator structures formed by oxygen implantation into silicon. Methodology; Determination of the concentration of chromium; Examination of the diffusion of copper and chromium in silicon.

Presents a study which developed an improved technique for seeded laser recrystallization of silicon-on-insulator stripes using a slanted elliptical beam and a computer-controlled system to register laser scans to alignment marks on the silicon wafer. Details on the recrystallization apparatus used; Fabrication of experimental structure; Results of the study.

Presents a study which examined the local and long-range pattern sensitivities of selective Si[sub1-x]Ge[subx] chemical vapor deposition. Comparison of the observed behavior with the easier lateral transport of reactive species in the gas phase at lower pressures; Effect of pressure on pattern sensitivity; Discussion on the effect of adding hydrochloric acid in the oxide.

Presents a study which examined the wafer temperature during chemical vapor deposition of a polycrystalline-silicon layer in a lamp-heated, rapid thermal processor using thermocouple-instrumented wafer. Experimental procedure; Results and discussion; Conclusions.

Presents a study that placed a SiGe/Si superlattice between the initial silicon surface layer and the subsequently grown silicon epitaxial layer in an attempt to reduce density of threading dislocations in a silicon epitaxial layer grown on a separation by implantation of oxide structure. Parameters of molecular-beam epitaxy layers; Effect of the superlattice on the dislocations; Effect of subsequent heat treatments on the dislocations and the superlattice structure.