Bare Si Substrate Research Articles

One-dimensional gallium nitride micro/nanostructures synthesized by a space-confined growth technique

Hexagonal GaN prismatic sub-micro rods and cone nanowires have been synthesized in a large scale by a novel and controllable space-confined growth method. The as-synthesized GaN products are highly crystalline with a wurtzite structure. The prismatic rods have lengths of 15∼20 μm and diameters of 400∼500 nm enclosed by hexagonal smooth side surfaces and a pyramidal end. And the cone nanowires have average diameters of 150∼200 nm and lengths up to several tens of μm with a cone tip. The photoluminescence (PL) studies reveal prominent band-gap UV emission properties of GaN products and narrow FWHM, indicating the excellent luminescent performance and high crystal quality. For field emission characteristic of GaN nanowires, the turn-on field is about 9.5 V/μm and the current density reaches 1.0 mA/cm2 at an electric field of 18 V/ μm. The contrast experiments indicate a novel growth control can be achieved by using a graphite tube as reaction vessel. The sealed graphite tube combined with metallic initiator is greatly responsible for large-scale and uniform preparation of GaN prismatic rods and cone nanowires. Highly symmetric GaN hexagonal micropyramids are grown on a bare Si substrate. The growth mechanism and the control function of the graphite tube are demonstrated. These low-dimensional structures not only enrich semiconducting GaN family, but also are good building blocks for optoelectronic devices.

Selective growth of β-SiC whisker on a patterned Si (111) substrate for a field emission device

β-SiC whiskers were grown via a vapor-solid (VS) reaction on two types of substrates; bare Si (111) and SiO 2-coated Si (111). Different growth behaviors of β-SiC whiskers were observed for each substrate. β-SiC whiskers grew only on the bare Si substrate, not on the SiO 2-coated Si surface. Therefore, β-SiC whiskers could be selectively grown along the patterns on the SiO 2-coated Si substrate. The turn-on field and the maximum current density of the specimens using selectively grown whiskers along the patterns on the SiO 2-coated Si substrate were 2.0 V/μm and 1.01 mA/cm 2, respectively. The converted curve of I– V characteristics of β-SiC whiskers by the Fowler–Nordheim equation maintained a linear slope.

Homoepitaxial Growth of Vertical Si Nanowires on Si(100) Substrate using Anodic Aluminum Oxide Template

ABSTRACTHomo-epitaxial growth of Si nanowires on Si (100) substrate was accomplished using a combination of anodic aluminum oxide (AAO) template and Vapor-Liquid-Solid (VLS) growth. We prepared two types of AAO template for epitaxial growth of Si nanowires.We observed vertically grown epitaxial Si (100) nanowires in the AAO template. In addition, after leaving filled pores, Si nanowires changed their growth direction from [100] to <111>. This result shows that the walls of the pores forced the growth direction of Si nanowires parallel to the direction of the pores, and after complete filling, the growth direction changes to that of the Si nanowires on a bare Si substrate.

Growth of carbon nanotube bundle arrays on silicon surfaces

The growth on silicon substrates of arrayed bundles of multiwalled carbon nanotubes (CNTs) by metal catalyzed chemical vapor deposition of carbon from ethylene has been characterized and optimized. We find that, while CNTs can grow on bare Si substrates, the growth is substantially more reproducible if a thin (∼3nm) barrier layer of aluminum oxide is used between the Si surface and iron catalyst. Optimum Fe thickness and growth temperature are 3.0 nm and 650 °C, respectively. We find that the CNT length increases linearly with time at a rate of 3–4μm∕min for up to 2 h of CNT growth, after which the growth ceases. The length of the resulting CNT can thus be controlled up to a maximum length of ∼500μm. Such control over CNT bundle length will be crucial in the incorporation of these bundle arrays into high-intensity electron field emission devices.

Wurtzite GaN nanocolumns grown on Si(001) by molecular beam epitaxy

Wurtzite single crystal GaN nanocolumns were grown by plasma-assisted molecular beam epitaxy on bare Si(001) substrates. Nanocolumns with diameters in the range of 20–40nm have no traces of extended defects and they grow aligned along the [0001] direction. Photoluminescence measurements in nanocolumns evidence a very high crystal quality in terms of intense and narrow excitonic emissions. Raman scattering data show that the nanocolumns are strain-free. These results open the way to an efficient integration of optoelectronic devices with the complementary metal oxide semiconductor technology.

Low Pressure RF Plasma Jet Sputtering Technique Applied to Ferroelectric Films: Ba<sub>1-x</sub> Sr<sub>x</sub>TiO<sub>3</sub>

Technology aspects and characterization of BaxSr1-xTiO3 (BST) films fabricated with low pressure plasma jet technique are presented. BST films were deposited on silicon coated with Pt/TiO2/SiO2 and on bare Si substrates. The nozzles-type RF hollow cathode has been fabricated from hot pressed BaTiO3, SrTiO3, and BST ceramics. Controlling of RF voltage, RF current and substrate temperature allowed us to deposit reproducible films with controlled grain size. Hysteresis loops, ellipsometric and micro-Raman investigation results are presented and discussed.

Comparison of Thermal Stability and Chemical Bonding Configurations of Plasma Oxynitrided Hf and Zr Thin Films

In this work, we study the characteristics of plasma oxynitrided Hf and Zr thin films. A 5-nm-thick Hf or Zr metal film is deposited on the bare Si substrate, followed by plasma oxynitridation on these metal films in a or ambient. Incorporation of O and N leads to the formation of and films. The high nitrogen content in the films prepared by plasma oxynitridation is found to increase the onset of the crystallization temperature, as compared to films prepared by plasma oxynitridation. Nevertheless, the difference in crystallization temperature is not seen for films. The interlayer (IL) between (or ) and Si is found to be thinner for the films with plasma oxynitridation than those with plasma oxynitridation. However, the nitrogen incorporated by plasma oxynitridation appears to be depleted after rapid thermal oxidation annealing and is not effective to inhibit the growth of the IL. The activation energy of the IL growth for and oxynitrided is 0.23 and 0.13 eV, respectively. The activation energy of the IL growth for and oxynitrided is 0.19 and 0.14 eV, respectively.

Growth of β-SiC nanowires and thin films by metalorganic chemical vapor deposition using dichloromethylvinylsilane

We deposited β-SiC thin films and β-SiC nanowires by metalorganic chemical vapor deposition (MOCVD) on bare Si(100) and Ni-coated Si(100) substrates using dichloromethylvinylsilane [CH2CHSi(CH3)Cl2] as a single molecular precursor. Deposition pressures and temperatures were about 50 mTorr and 800–1200 °C, respectively, and deposition durations were 0.5–2 h. Nickel plays an important role as a catalyst in growing β-SiC nanowires. As-deposited zinc-blende SiC thin films and nanowires were grown separately. Initial growth rates are strongly dependent on deposition temperature. TEM analysis showed that the as-deposited β-SiC nanowires are wrapped with very thin amorphous carbon layers, have a [111] growth direction with well-crystallized structure, and modulated diameters. XPS and EDX analyses show that the Si:C compositions are about 1.0:1.2, suggesting possible applications to both field emitters and electronic devices.

Ultrafine Platinum Nanoparticles Uniformly Dispersed on Arrayed CNx Nanotubes with High Electrochemical Activity

The structure and electrochemical properties of arrayed nitrogen-containing carbon nanotube (CNx NT)−platinum nanoparticle (Pt NP) composites directly grown on Si substrates have been investigated. The CNx nanotube arrays were grown by microwave-plasma-enhanced chemical vapor deposition first and then acted as the template and support for Pt dispersion in the following sputtering process. Under the same sputtering conditions, it was found that well-separated Pt NPs would form with an average diameter of 2 nm on the arrayed NTs while a continuous Pt thin film was observed on the bare Si substrate. X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and electron microscopy were employed to study bonding and structure changes with increasing deposition time. Implications of the C1s and N1s bonding changes in XPS and their possible relation to the NT−Pt composite structures with self-limited size distribution are discussed. Cyclic voltammograms show well-behaved curves in methanol oxidation, suggesting an efficient electronic conduction mechanism from the substrate via CNx NTs to reach individual Pt NPs is in operation. Such an integrated nanocomposite approach possesses a high potential for micro direct methanol fuel cell applications.

Fabrication and ferroelectric studies of (Bi, Gd)4Ti3O12 thin films grown on Pt/Ti/SiO2/Si and p-type Si substrates

Lead-free bismuth-layered perovskite ferroelectric Bi3.4Gd0.6Ti3O12 (BGT) thin films have been successfully deposited on Pt(111)/Ti/SiO2/Si and p-type Si(100) substrates by a sol–gel spin-coating process followed by annealing. The formation of BGT thin film was found to be sensitive to the annealing temperatures. The remanent polarization (2Pr) and coercive field (2Ec) of the metal–ferroelectrics–metal capacitor using a BGT film deposited on Pt(111)/Ti/SiO2/Si by annealing at 700°C were 49.6μC/cm2 and 249kV/cm, respectively, with 260kV/cm of applied field. The BGT film exhibits a good fatigue resistance up to 1.45×1010 switching cycles at a frequency of 1MHz.The metal–ferroelectrics–semiconductor type capacitor using a BGT film grown on a bare p-type Si(100) substrate exhibits a good capacitance–voltage (C–V) characteristics. By changing AC frequencies from 1kHz to 10MHz, the C–V characteristics, including total capacitance and memory window (∼1V), were not affected. The temperature dependency of C–V and I–V characteristics for the MFS type capacitor were interpreted in terms of a new anomalous thin layer between the BGT thin film and the p-type Si(100) substrate.

Growth and properties of (0 0 1)-oriented Pb(Zr 0.52Ti 0.48)O 3/LaNiO 3 films on Si(0 0 1) substrates with TiN buffer layers

Pulsed laser deposition has been used to grow Pb(Zr 0.52Ti 0.48)O 3 (PZT)/LaNiO 3 (LNO) bilayer thin films on bare Si(0 0 1) and SiO 2-coated Si(0 0 1) substrates coated with TiN buffer layers. The effect of background gas pressure on the crystallographic texture of the polycrystalline thin films has been investigated in detail. XRD analysis shows that under optimized conditions, (0 0 1)-oriented PZT/LNO/TiN heterostructures can be grown on both Si(0 0 1) and SiO 2/Si substrates. SIMS measurement indicates that there is no inter-diffusion or chemical reaction at PZT/LNO interface, while La and Ni can inward diffuse into the TiN layers. The (0 0 1)-textured PZT films have remnant polarizations as high as 23 μC/cm 2 and low coercive fields. Up to 10 10 polarization switching cycles have been achieved in these PZT films.

Atomic-layer-deposited Al2O3 thin films with thin SiO2 layers grown by in situ O3 oxidation

The growth, thermal annealing behaviors, and electrical properties of Al2O3 thin films grown by atomic layer deposition (ALD) on bare (100)Si and various oxidized Si wafers, by in situ O3 oxidation at 400°C and ex situ rapid thermal annealing (RTA) under O2 atmosphere at 900°C, were investigated. The ALD process was performed using Al(CH3)3 and high concentration of O3(400gm3). The high oxidation potential of O3 oxidized the Si surface at a very early stage of film growth and eliminated the incubation period even on a bare Si surface. The as-grown Al2O3 films had excess oxygen in the films, which diffused to the film Si interface and increased the interfacial layer by oxidizing the Si substrates during postannealing. The Al2O3 films grown on a bare Si substrate had the highest concentration of excess oxygen which resulted in the largest increase in the interfacial layer thickness during postannealing. As a result, the initial oxidation of the Si wafer did not significantly decrease the capacitance density compared to the films grown on a nonoxidized Si wafer at the as-deposited and postannealed states. Therefore, the Al2O3 layers grown using a high concentration of O3 oxidant on the in situ O3 oxidized Si wafers showed real high-k gate dielectric performance although the dielectric constants of the Al2O3 films were rather small (∼9) compared to other high-k gate dielectric films.

Growth and polarization feature studies on rapid thermally processed preferentially c-axis-oriented Bi 4Ti 3O 12 thin films on Si by sol–gel

Crack free Bi 4Ti 3O 12 ferroelectric films were fabricated by sol–gel method with rapid thermal annealing (RTA) techniques on p-Si and Pt/Ti/SiO 2/p-Si substrates. The effects of annealing temperature and time on microstructure, growth behavior and polarization feature of Bi 4Ti 3O 12 films were investigated. The patterns of X-ray diffraction (XRD) exhibited that Bi 4Ti 3O 12 film on bare Si substrates is c-axis-orientation with the increase of annealing temperature and without any pyrochlore phase or other second phase, but Bi 4Ti 3O 12 film on Pt/Ti/SiO 2/p-Si substrate is not c-axis-orientation and there is pyrochlore phase in it. Annealing time of 5 min is enough to attain perovskite phase at 550 °C and highly c-axis-oriented Bi 4Ti 3O 12 films can be obtained at 850 °C, but the compatible annealing temperature for best ferroelectric properties with a remanent polarization of 8.44 μC/cm 2 is 700 °C. The cross-sectional SEM photographs and the capacitance-voltage ( C– V) curve of Ag/Bi 4Ti 3O 12/p-Si demonstrate that the good interface characteristics of Bi 4Ti 3O 12/p-Si can be obtained by sol–gel method with rapid thermal annealing techniques, which suggests that the Ag/Bi 4Ti 3O 12/p-Si configuration is promising for memory applications.

The influence of metal aluminium on the reduction of theSm3+ doped in aluminosilicate glass films

Sm3+-doped glass sol was prepared by a sol–gel method and coated on a bareSi substrate and an Al coated Si substrate (Al/Si). The coated glassfilms were heat treated in a hydrogen atmosphere or air to reduce theSm3+ toSm2+ and then the optical properties were examined through a photoluminescence(PL) experiment. While the glass films coated on a bare Si substrate or an Al/Sione were well reduced in hydrogen atmosphere, only the glass films coated onthe Al/Si substrate were reduced in air. We thus suggest two possible reducingmechanisms related to hydrogen and the metal aluminium and we found that the metalaluminium coated on a Si substrate plays an important role in the reducing process.

Epitaxial lithium fluoride films grown by pulsed laser deposition

Lithium fluoride (LiF) films have been prepared on LaAlO3 (LAO), MgO, Si and TiN buffered Si substrates using a pulsed laser deposition (PLD) technique. Their surface morphology and structural qualities were studied by using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Those films deposited on (100)MgO and (100)TiN buffered Si exhibited (200)LiF||(200)MgOand(200)LiF||(200)TiN||(200)Si epitaxial relationships, respectively. These results suggest that LiF films can be epitaxially grown on lattice match substrates and, for the first time, on (100)Si via a buffer layer. LiF grown on bare (100)Si and (100)LAO substrates, however, yielded films of (100) preferred orientation only. Lattice mismatch and thermal effects are invoked to explain these observations. The surfaces of the LiF films are very rough and covered with large globules due to splashing of molten droplets from the target. In order to remedy such deficiencies we used a shadow mask to reduce both the size and the number of these globules while maintaining the heteroepitaxial properties. As a result optically smooth LiF films of excellent structural quality are produced.

Organic Low-k Dielectric Material Etching by CH3NH2/N2 Plasma

An etching process has been developed for an organic low-k dielectric material, FLARE, that uses a gas chemistry of CH3NH2/N2 in a magnetic neutral loop discharge (NLD) plasma system. The organic low-k etching can provide a normal-taper profile with no micro-trenching and little hard-mask erosion, which are necessary for fabricating Cu/organic low-k damascene multilevel interconnects. Inverse reactive ion etching (RIE) lag was observed under conditions that produced the normal-taper profile. We evaluated the amount of ions and radicals generated in CH3NH2/N2, CH4/N2, and H2/N2 plasmas by means of quadrupole mass spectrometry (QMS) and analyzed films deposited on a bare Si substrate in CH3NH2/N2, CH4/N2, and H2/N2 plasmas by using X-ray photoelectron spectroscopy (XPS). We found that a normal-taper etching profile was obtained when the C/N concentration ratio of the deposited film was about 2–3 in the CH3NH2/N2 plasma.

Microstructure and magnetic properties of hexagonal barium ferrite thin films with various underlayers

BaM (barium ferrite) thin films and underlayers (Fe, Cr, Al2O3, Fe2O3, ZnFe2O4, TiO2) were prepared by rf/dc magnetron sputtering on (100) oriented bare Si substrates. The effects of the underlayer on grain orientation, magnetic properties, and microtexture of BaM film were studied. All the BaM films, except BaM/Fe/Si film, attained nearly the same perpendicular and in-plane coercivities. The BaM/TiO2/Si exhibits the highest coercivity. However, regardless of the underlayer, BaM grains are randomly oriented. By adopting ZnFe2O4 as an underlayer, the interdiffusion of Si from substrate was prohibited to some degree. Elongated grains from the extinction of small platelet grains were grown with an increase in the BaM film thickness of BaM/Si. The microstructure of BaM in BaM/TiO2/Si was strongly dependent on both the microstructure of TiO2 underlayer and the total sputtering gas pressure.

NANOCRYSTALLINE DIAMOND THIN FILMS AS INFRARED OPTICAL PROTECTIVE COATINGS

Nanocrystalline diamond thin films have been grown on both sides of Si wafer by microwave plasma-enhanced chemical vapor deposition using a mixture of CH4 and H2 as source gas. It was shown that infrared transmission of Si has been greatly enhanced and the maximum transmittance reaches 85%. By optimizing the film thickness, we can obtain the maximum increment in the desired infrared wavelength range. Sand spraying test showed that, while the bare Si substrate exhibited obvious surface damage, no damage could be observed on the diamond surface after the sand spraying. The results confirm that the nanocrystalline diamond films coated on Si can not only increase the infrared transmission but also act as a protective coating.

FABRICATION OF Si NANOCOLUMNS AND Si SQUARE SPIRALS ON SELF-ASSEMBLED MONOLAYER COLLOID SUBSTRATES

Amorphous silicon nanocolumns, square nanospirals, and multilayer spiral/column rods are fabricated on bare Si substrates and monolayer colloid substrates by glancing angle deposition. The grown films are studied by scanning electron microscopy and transmission electron microscopy. The size of the deposited Si columns and spirals increases with the size of colloid particles for fixed incident angle of deposition flux. The feasibility of fabricating separated, well-ordered square spirals provides a cost effective and simple way to fabricate photonic crystals.

A High-Temperature STM-Study of Iron Silicide Formation on High Index Silicon Surfaces

AbstractThe nucleation and initial growth of iron silicide on Si(113), Si(5 5 12) and Si(114) is studied using high temperature STM. During MBE and gas source deposition (precursor Fe(CO)5 STM-“movies” at temperatures up to 600°C directly show the kinetics of silicide formation on the surface. A complete 2D-wetting layer is formed on all vicinal surfaces for temperatures below 510°C. A chain-like silicide structure with a mixture of different periodicities (4×n), with n ranging from 2-6, is found. Above one monolayer growth proceeds with anisotropic 3D-silicide-islands. The wetting layer was found to be only metastable at lower growth temperature. At temperatures above 510°C the 2D-silicide layer does not wet the substrate anymore. In the equilibrium growth mode, 3D-islands directly grow on the bare Si-substrate. The anisotropy of the 3D-islands is extremly temperature dependent resulting in an aspect ratio up to 50 at 600°C. Especially on Si(114) a one-dimensionally nanostructured silicide layer can be grown in this way. A lateral spreading of the 3D-islands forming an interconnected silicide layer is achieved on Si(113) by a stochiometric codeposition of Fe and Si.