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 m and D = 39 to 400 nm, respectively. The wires showed resonant frequencies in the f 0 =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 / L 2 , yielded a ratio of ͱ E / = 9400Ϯ 450 m / s. Assuming a density of = 2330 kg/ m 3 , this experimental result yields an experimental Young modulus of E = 205Ϯ 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 10 2 Torr, suggesting that viscous damping does not dominate the dissipative processes in this pressure range. Although viscous damping became important above P =10 2 Torr, relatively high quality factors of Q = 7000 were still observed at atmospheric pressure.

Using compositionally graded buffers, we demonstrate InP on GaAs suitable for minority carrier devices, exhibiting a threading dislocation density of 1.2×106∕cm2 determined by plan-view transmission electron microscopy. To further quantify the quality of this InP on GaAs, a photoluminescence (PL) structure was grown to compare the InP on graded buffer quality to bulk InP. Comparable room and low temperature (20K) PL was attained. (The intensity from the PL structure grown on the InP on GaAs was ∼70% of that on bulk InP at both temperatures.) To achieve this, graded buffers in the InGaAs, InGaP, InAlAs, and InGaAlAs materials systems were explored. In each of these systems, under certain growth conditions, microscopic compositional inhomogeneities blocked dislocation glide and led to threading dislocation densities sometimes >109∕cm2. These composition variations are caused by surface-driven, phase separated, Ga-rich regions. As the phase separation blocked dislocation glide and led to high threading dislocation densities, conditions for avoiding phase separation were explored and identified. Composition variations could be prevented in InxGa1−xAs graded buffers grown at 725°C to yield low dislocation densities of 9×105∕cm2 for x<0.34, accommodating ∼70% of the lattice mismatch between GaAs and InP. Compositional grading in the InyGa1−yP (0.8<y<1.0) materials system grown at 700°C was found to accommodate the remaining lattice mismatch to achieve high-quality InP on GaAs with little rise in threading dislocation density by avoiding phase separation.

We report a structure to control nanowire location and growth direction and demonstrate top-gated, metal-oxide-semiconductor, field-effect transistors (MOSFETs) using this structure. The nanowires wereengineered to grow against an oxide surface of a (001), silicon-on-insulator substrate, enabling straightforward fabrication of MOSFETs exhibiting an Io/Ioff ratio approximately 104 and a subthreshold slope of approximately 155 mV/decade. Though nanowires were engineered to grow in (110) directions, the nanowires still grew by the addition of {111) planes.

Single-crystalline Si nanotubes (NTs) were fabricated using vapor-liquid-solid grown, Ge nanowires (NWs) as a template upon which a Si shell was deposited to first grow Ge-core, Si-shell NWs. The tips of these NWs were removed, enabling exposure of the Ge core to H(2)SO(4) and H(2)O(2). After removing the Ge core, single-crystalline Si NTs remained. In addition to growing these Ge-core, Si-shell NWs from a Si (111) substrate, these NWs were also grown horizontally from a vertical Si surface to enable the fabrication of horizontal NTs after focused ion-beam cutting and etching steps. The resonant properties of the Ge-core, Si-shell NW, and the Si NT after the cutting and etching steps were measured and found to have a quality factor, Q, of approximately 1800.