Controllable chemical vapor deposition of large area uniform nanocrystalline graphene directly on silicon dioxide

Metal-catalyst-free chemical vapor deposition (CVD) of large area uniform nanocrystalline graphene on oxidized silicon substrates is demonstrated. The material grows slowly, allowing for thickness control down to monolayer graphene. The as-grown thin films are continuous with no observable pinholes, and are smooth and uniform across whole wafers, as inspected by optical-, scanning electron-, and atomic force microscopy. The sp 2 hybridized carbon structure is confirmed by Raman spectroscopy. Room temperature electrical measurements show ohmic behavior (sheet resistance similar to exfoliated graphene) and up to 13 of electric-field effect. The Hall mobility is ∼40 cm 2/Vs, which is an order of magnitude higher than previously reported values for nanocrystalline graphene. Transmission electron microscopy, Raman spectroscopy, and transport measurements indicate a graphene crystalline domain size ∼10 nm. The absence of transfer to another substrate allows avoidance of wrinkles, holes, and etching residues which are usually detrimental to device performance. This work provides a broader perspective of graphene CVD and shows a viable route toward applications involving transparent electrodes. © 2012 American Institute of Physics.

Rapid Electron Beam Reacted Tantalum/Titanium Bilayers on Silicon : Semiconductors and Semiconductor Devices

The electrical and structural characteristics of tantalum-titanium bilayers on silicon reacted by electron beam heating have been investigated over a wide range of temperature and time conditions. The reacted layers exhibit low sheet resistance and stable electrical characteristics up to at least 1100℃. Titanium starts reacting from 750℃ onwards for 100 milliseconds reaction times whereas tantalum starts reacting only above 900℃ for such short reaction times. RBS results confirm that silicon is the major diffusing species and there is no evidence for the formation of ternary silicides. Reactions have also been explored on millisecond time scales by non-isothermal heating.

Plasma stabilisation of metallic nanoparticles on silicon for the growth of carbon nanotubes

Ammonia (NH 3) plasma pretreatment is used to form and temporarily reduce the mobility of Ni, Co, or Fe nanoparticles on boron-doped mono- and poly-crystalline silicon. X-ray photoemission spectroscopy proves that NH 3 plasma nitrides the Si supports during nanoparticle formation which prevents excessive nanoparticle sintering/diffusion into the bulk of Si during carbon nanotube growth by chemical vapour deposition. The nitridation of Si thus leads to nanotube vertical alignment and the growth of nanotube forests by root growth mechanism. © 2012 American Institute of Physics.

Hydrogen sensor based on silicon carbide (SiC) MOS capacitor

Silicon carbide (SiC) based MOS capacitor devices are used for gas sensing in high temperature and chemically reactive environments. A SiC MOS capacitor structure used as hydrogen sensor is defined and simulated. The effects of hydrogen concentration, temperature and interface traps on C-V characteristics were analysed. A comparison between structures with different oxide layer types (SiO2, TiO2 and ZnO) and thicknesses (50..10nm) was conducted. The TiO2 based structure has better performance than the SiO2 and ZnO structures. Also, the performance of the SiC MOS capacitor increases at thinner oxide layers. © 2012 IEEE.

Enhanced down conversion of photons emitted by photoexcited Er xY2-xSi2O7 films grown on silicon

Photon cutting with efficiencies up to 400% is demonstrated in Erx Y2-x Si2 O7 films grown on Si and its concentration dependence is analyzed. The cutting is the result of cross-energy-transfer processes occurring within a single rare earth (Er3+) acting as both sensitizer and activator. Similarities with upconversion are revealed and possible applications in solar cells are discussed. © 2010 The American Physical Society.

Precursor flow rate manipulation for the controlled fabrication of twin-free GaAs nanowires on silicon substrates

Vertically oriented GaAs nanowires (NWs) are grown on Si(111) substrates using metal-organic chemical vapor deposition. Controlled epitaxial growth along the 111 direction is demonstrated following the deposition of thin GaAs buffer layers and the elimination of structural defects, such as twin defects and stacking faults, is found for high growth rates. By systematically manipulating the AsH 3 (group-V) and TMGa (group-III) precursor flow rates, it is found that the TMGa flow rate has the most significant effect on the nanowire quality. After capping the minimal tapering and twin-free GaAs NWs with an AlGaAs shell, long exciton lifetimes (over 700ps) are obtained for high TMGa flow rate samples. It is observed that the Ga adatom concentration significantly affects the growth of GaAs NWs, with a high concentration and rapid growth leading to desirable characteristics for optoelectronic nanowire device applications including improved morphology, crystal structure and optical performance. © 2012 IOP Publishing Ltd.

Taper-free and kinked germanium nanowires grown on silicon via purging and the two-temperature process

We investigate the growth procedures for achieving taper-free and kinked germanium nanowires epitaxially grown on silicon substrates by chemical vapor deposition. Singly and multiply kinked germanium nanowires consisting of 111 segments were formed by employing a reactant gas purging process. Unlike non-epitaxial kinked nanowires, a two-temperature process is necessary to maintain the taper-free nature of segments in our kinked germanium nanowires on silicon. As an application, nanobridges formed between (111) side walls of V-grooved (100) silicon substrates have been demonstrated. © 2012 IOP Publishing Ltd.

Vertically oriented epitaxial germanium nanowires on silicon substrates using thin germanium buffer layers.

We demonstrate a method to realize vertically oriented Ge nanowires on Si(111) substrates. Ge nanowires were grown by chemical vapor deposition using Au nanoparticles to seed nanowire growth via a vapor-liquid-solid growth mechanism. Rapid oxidation of Si during Au nanoparticle application inhibits the growth of vertically oriented Ge nanowires directly on Si. The present method employs thin Ge buffer layers grown at low temperature less than 600 degrees C to circumvent the oxidation problem. By using a thin Ge buffer layer with root-mean-square roughness of approximately 2 nm, the yield of vertically oriented Ge nanowires is as high as 96.3%. This yield is comparable to that of homoepitaxial Ge nanowires. Furthermore, branched Ge nanowires could be successfully grown on these vertically oriented Ge nanowires by a secondary seeding technique. Since the buffer layers are grown under moderate conditions without any high temperature processing steps, this method has a wide process window highly suitable for Si-based microelectronics.

Assembly and inspection of liquid crystal on silicon devices

Liquid crystal on silicon (LCOS) is one of the most exciting technologies, combining the optical modulation characteristics of liquid crystals with the power and compactness of a silicon backplane. The objective of our work is to improve cell assembly and inspection methods by introducing new equipment for automated assembly and by using an optical inspection microscope. A Suss-MicroTec Universal device bonder is used for precision assembly and device packaging and an Olympus BX51 high resolution microscope is employed for device inspection. © 2009 Optical Society of America.

Sub-nanosecond optical switch based on silicon racetrack resonator

We experimentally demonstrate a small-size and high-speed silicon optical switch based on the free carrier plasma dispersion in silicon. Using an embedded racetrack resonator with a quality factor of 7400, the optical switch shows an extinction ratio exceeding 13 dB with a footprint of only 2.2 x 10(-3) mm(2). Moreover, a novel pre-emphasis technique is introduced to improve the optical response performance and the rise and the fall times are reduced down to 0.24 ns and 0.42 ns respectively, which are 25% and 44% lower than those without the pre-emphasis.

Flexible Control of Light Propagation Using a Novel Photonic Crystal Hetero-Waveguide Based on Silicon-on-Insulator Slab

We demonstrate a photonic crystal hetero-waveguide based on silicon-on-insulator (SOI) slab, consisting of two serially connected width-reduced photonic crystal waveguides with different radii of the air holes adjacent to the waveguide. We show theoretically that the transmission window of the structure corresponds to the transmission range common to both waveguides and it is in inverse proportion to the discrepancy between the two waveguides. Also the group velocity of guided mode can be changed from low to high or high to low, depending on which port of the structure the signal is input from just in the same device, and the variation is proportional to the discrepancy between the two waveguides. Using this novel structure, we realize flexible control of transmission window and group velocity of guided mode simultaneously.

Interface as the origin of ferromagnetism in cobalt doped ZnO film grown on silicon substrate

We have investigated the magnetic properties of Co-doped zinc oxide (ZnO) film deposited on silicon substrate by magnetron sputtering. Co ions have a valence of 2+ and substitute for Zn sites in the lattice. By using a chemical etching method, an extrinsic ferromagnetism was demonstrated. The observed ferromagnetism is neither associated with magnetic precipitates nor with contamination, but originates from the silicon/silicon oxide interface. This interface ferromagnetism is characterized by being temperature independent and by having a parallel magnetic anisotropy. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2989128]

A ministop band in a single-defect photonic crystal waveguide based on silicon on insulator

This paper reports that a two-dimensional single-defect photonic crystal waveguide in the F-K direction with triangular lattice on a silicon-on-insulator substrate is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. A ministop band (MSB) is observed by the measurement of transmission characteristics. It results from the coupling between the two modes with the same symmetry, which is analysed from the stimulated band diagram by the effective index and the two-dimensional plane wave expansion methods. The parameter working on the MSB is the ratio of the radius of air holes to the lattice constant, r/a. It is obtained that the critical r/a value determining the occurrence or disappearance of MSB is 0.36. When r/a is larger than or equal to 0.36, the MSB occurs. However, when r/a is smaller than 0.36, the MSB disappears.

Enhanced infrared emission from colloidal HgTe nanocrystal quantum dots on silicon-on-insulator photonic crystals

A two dimensional silicon-on-insulator based photonic crystal structure is used to enhance the emission from colloidal HgTe nanocrystal quantum dots embedded in a thin polymer film. The enhancement is resonant to the leaky eigenmodes of the photonic crystals due to coherent scattering effects. Transmittance and photoluminescence experiments are presented to map the leaky mode dispersion and the angle dependence of the emission enhancement factor, which reaches values up to 80 (650) for vertical (oblique) emission in the telecommunication wavelength range.

EPITAXIAL LATERAL OVERGROWTH OF GaN ON SILICON-ON-INSULATOR

From a single process, GaN layers were laterally overgrown on maskless stripe-patterned (111) silicon-on-insulator (SOI) substrates by metalorganic chemical vapor deposition. The influence of stress on the behavior of dislocations at the coalescence during growth was observed using transmission electron microscopy (TEM). Improvement of the crystallin equality of the GaN layer was demonstrated by TEM and micro-Raman spectroscopy. Furthermore, the benefits of SOI substrates for GaN growth are also discussed.