Large area microwave plasma CVD of diamond using composite right/left-handed materials

Diamond growth at low temperatures (≤400 °C) and over large areas is attractive for materials, which are sensitive to high temperatures and require good electronic, chemical or surface tribological properties. Resonant-cavity microwave plasma enhanced (MWPE) chemical vapor deposition (CVD) is a standard method for growing diamonds, however, with limited deposition area. An alternative method for CVD of diamond over large area and at low temperature is to use a surface wave plasma (SWP). In this work we introduce a novel method to excite SWP using composite right/left-handed (CRLH) materials and demonstrate growth of nanocrystalline diamond (NCD) on 4-inch Si wafers. The method uses a set of slotted CRLH waveguides coupled to a resonant launcher, which is connected to a deposition chamber. Each CRLH waveguide supports infinite wavelength propagation and consists of a chain of periodically cascaded unit cells. The SWP is excited by a set of slots placed to interrupt large area surface current on the resonant launcher. This configuration yields a uniform gas discharge distribution. We achieve 80 nm/h growth rate for NCD films with a low surface roughness (5–10 nm) at 395 °C and 0.5 mbar pressure using a H2/CH4/CO2 gas mixture.publishedVersio

Growth, structural and plasma illumination properties of nanocrystalline diamond-decoratedgraphene nanoflakes

Decorating graphene nanoflakes with nanocrystalline diamond gives superior functioning for microplasma devices with long lifetime stability plasma illumination performances.</p

Large area microwave plasma CVD of diamond using composite right/left-handed materials

Diamond growth at low temperatures (≤400 °C) and over large areas is attractive for materials, which are sensitive to high temperatures and require good electronic, chemical or surface tribological properties. Resonant-cavity microwave plasma enhanced (MWPE) chemical vapor deposition (CVD) is a standard method for growing diamonds, however, with limited deposition area. An alternative method for CVD of diamond over large area and at low temperature is to use a surface wave plasma (SWP). In this work we introduce a novel method to excite SWP using composite right/left-handed (CRLH) materials and demonstrate growth of nanocrystalline diamond (NCD) on 4-inch Si wafers. The method uses a set of slotted CRLH waveguides coupled to a resonant launcher, which is connected to a deposition chamber. Each CRLH waveguide supports infinite wavelength propagation and consists of a chain of periodically cascaded unit cells. The SWP is excited by a set of slots placed to interrupt large area surface current on the resonant launcher. This configuration yields a uniform gas discharge distribution. We achieve 80 nm/h growth rate for NCD films with a low surface roughness (5–10 nm) at 395 °C and 0.5 mbar pressure using a H2/CH4/CO2 gas mixture

A1N on nanocrystalline diamond piezoelectric cantilevers for sensors/actuators

Micro-cantilevers can be used as both sensors and actuators. In this work, the design, fabrication and characterization of piezoelectrically driven nano-crystalline diamond (NCD) cantilevers are reported Diamond films were grown on silicon (100) substrates by microwave plasma enhanced chemical vapor deposition (MW-PECVD). Cantilevers are coated by DC pulsed piezoelectric with AlN films that is sandwiched between two metallic electrodes. The thicknesses of AlN and diamond layers are 1μm and 700nm, respectively. The influence on the electromechanical response of cantilevers length was studied. The motion of the electrically driven cantilevers is performed by measuring the evolution of the electrical impedance at the resonant frequencies that varies between 10 kHz and 130 kHz for the resonant mode. © 2009.status: publishe

Controlled boron content in lightly B doped single crystal diamond films by variation of methane concentration

Obtaining desirable electrical properties from B doped single crystal diamond SCD films hinges on precise control of boron incorporation into the crystal lattice structure. In this study, the impact of methane concentration during plasma deposition on boron incorporation of lightly B doped SCD films is investigated. SCD layers are grown successively by microwave plasma enhanced chemical vapor deposition CVD at different methane to hydrogen concentrations 1 , 2 , and 3 , with residual boron atoms present in the CVD reactor. An increase in methane concentration leads to surface defects such as unepitaxial crystallites and pyramidal hillocks. The charge carrier mobility, electrical conductivity, and boron content of samples are evaluated and discussed. The temperature dependent mobility is analyzed through theoretical modeling, revealing dominant scattering mechanisms at different temperatures. At 300 K, the maximum hole mobility reached 1200 cm2 V s for the 1 methane concentration sample, transitioning to hopping conduction at lower temperatures. An increase in boron doping level with rising methane concentration is detected by Fourier transform infrared spectroscopy, cathodoluminescence spectroscopy, Hall effect, and X ray photoelectron spectroscopy measurements. These findings highlight the potential of methane concentration in plasma feedgas to control boron concentration in CVD diamond and open avenues for crafting efficient high power electronic applications using p type SCD film

Separation of intra- and intergranular magnetotransport properties in nanocrystalline diamond films on the metallic side of the metal-insulator transition

A systematic study on the morphology and electronic properties of thin heavily boron-doped nanocrystalline diamond (NCD) films is presented. The films have nominally the same thickness (≈150 nm) and are grown with a fixed B/C ratio (5000 ppm) but with different C/H ratios (0.5-5%) in the gas phase. The morphology of the films is investigated by x-ray diffraction and atomic force microscopy measurements, which confirm that lower C/H ratios lead to a larger average grain size. Magnetotransport measurements reveal a decrease in resistivity and a large increase in mobility, approaching the values obtained for single-crystal diamond as the average grain size of the films increases. In all films, the temperature dependence of resistivity decreases with larger grains and the charge carrier density and mobility are thermally activated. It is possible © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.status: publishe

Impact of methane concentration on surface morphology and boron incorporation of heavily boron-doped single crystal diamond layers

The methane concentration dependence of the plasma gas phase on surface morphology and boron incorporation in single crystal, boron-doped diamond deposition is experimentally and computationally investigated. Starting at 1%, an increase of the methane concentration results in an observable increase of the B-doping level up to 1.7 x 10(21) cm(-3), while the hole Hall carrier mobility decreases to 0.7 +/- 0.2 cm(2) V-1 s(-1). For B-doped SCD films grown at 1%, 2%, and 3% [CH4]/[H-2], the electrical conductivity and mobility show no temperature-dependent behavior due to the metallic-like conduction mechanism occurring beyond the Mott transition. First principles calculations are used to investigate the origin of the increased boron incorporation. While the increased formation of growth centers directly related to the methane concentration does not significantly change the adsorption energy of boron at nearby sites, they dramatically increase the formation of missing H defects acting as preferential boron incorporation sites, indirectly increasing the boron incorporation. This not only indicates that the optimized methane concentration possesses a large potential for controlling the boron concentration levels in the diamond, but also enables optimization of the growth morphology. The calculations provide a route to understand impurity incorporation in diamond on a general level, of great importance for color center formation. (C) 2020 Elsevier Ltd. All rights reserved.</p

Defect attributed variations of the photoconductivity and photoluminescence in the HVPE and MOCVD as-grown and irradiated GaN structures

The effect of native and radiation induced defects on the photoconductivity transients and photoluminescence spectra have been examined in GaN epitaxial layers of 2.5 and 12 μm thickness grown on bulk n-GaN/sapphire substrates by metal-organic chemical vapor deposition (MOCVD). For comparison, free-standing GaN as-grown samples of 500 μm thickness, fabricated by hydride vapor phase epitaxy (HVPE), were investigated. Manifestation of defects induced by 10-keV X-ray irradiation with the dose of 600 Mrad and 100-keV neutrons with the fluences of 5×1014 and 1016 cm−2 as well as of 24 GeV/c protons with fluence 1016 cm−2 have been revealed through contact photoconductivity and microwave absorption transients. The amplitude of the initial photoconductivity decay is significantly reduced by the native and radiation defects density. Synchronous decrease of the steady-state PL intensity of yellow, blue and ultraviolet bands peaked at 2.18, 2.85, and 3.42 eV, respectively, with density of radiation-induced defects is observed. The decrease of the PL intensity is accompanied by an increase of asymptotic decay lifetime in the photoconductivity transients, which is due to excess-carrier multi-trapping. The decay fits the stretched exponent approximation exp[-(t/τ)α] with the different factors α in as-grown material (α≈0.7) and irradiated samples (α≈0.3). The fracton dimension ds of disordered structure changes from 4.7 to 0.86 for as-grown and irradiated material, respectively, and it implies the percolative carrier motion on an infinite cluster of dislocations net in the as-grown material and cluster fragmentation into finite fractons after irradiations