• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.6
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• pp.215-219
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• 2016

Vanadium-doped SiC crystals have been grown by using a porous graphite inner crucible filled with vanadium carbide (VC) and by using a porous graphite plate and SiC + VC powders, respectively. Semi-insulating SiC crystals were grown onto the 6H-SiC seed crystals by PVT (Physical Vapor Transport) method. The grown crystals were indicated to be 6H-SiC polytype by XRD. As result of SIMS analysis, vanadium-rich precipitates were observed when the vanadium concentration was relatively higher than the maximum solubility of vanadium ($3-5{\times}10^{17}cm^{-3}$) in vanadium-doped SiC crystals, which resulted in degradation of crystal quality.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.2
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• pp.89-93
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• 2017

GaN single crystals were grown by controlling of various processing parameters such as growing temperature, V/III ratio and growing rate. We optimized thickness of bulk GaN single crystal by analyzing defect of surface and inside of the GaN single crystal for application to high brightness and power device. 2-inch bulk GaN single crystals were grown by HVPE (hydride vapor phase epitaxy) on sapphire and their thickness was 0.3~7.0 mm. Crystal structure of the grown bulk GaN was analyzed by XRD (X-ray diffraction). The surface characteristics of the grown bulk GaN were observed by OM (optical microscope) and SEM (scanning electron microscopy) with measuring EPD (etch pits density) of the GaN crystals.

• Korean Journal of Materials Research
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• v.8 no.7
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• pp.591-595
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• 1998

In this work, the freestanding GaN single crystalline substrates without cracks were grown by hydride vapor phase epitaxy (HVPE) and its some properties were investigated. The GaN substrate, having a current maximum size of 350 $\mu\textrm{m}$-thickness and 100$\textrm{mm}^2$ area, were obtained by HVPE growth of thick film GaN on sapphire substrate and subsequent mechanical removal of the sapphire substrate. A lattice constant of $C_o$= 5.18486 $\AA$ and a FWHM of DCXRD was 650 arcsec for the single crystalline GaN substrate. The low temperature PL spectrum consist of three excitonic emission and a deep D- A pair recombination at 1.8eV. The Raman E, (high) mode frequency was 567$cm^{-1}$ which was the same as that of strain free bulk single crystals. The Hall mobility and carrier concentration was 283$cm^3$<\ulcornerTEX>/ V.sand 1.1$\times$$10^{18}cm^{-3}$, respectively.

• Progress in Superconductivity and Cryogenics
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• v.16 no.3
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• pp.7-9
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• 2014

Single-crystal like $MgB_2$ thin film was grown on (000l) $Al_2O_3$ substrate by using hybrid physical-chemical vapor deposition (HPCVD) system. Single crystal properties were studied by X-ray diffraction (XRD) and the full width at half maximum (FWHM) of the (0001) $MgB_2$ peak is $15^{\circ}$, which is very close to that has been reported for $MgB_2$ single-crystal. It indicates that the crystalline quality of thin film is good. Temperature dependence on resistivity was investigated by physical property measurement system (PPMS) in various applied fields from 0 to 9 T. The upper critical field ($H_{c2}$) and irreversibility field ($H_{irr}$) were determined from PPMS data, and the estimated values are comparable with that of $MgB_2$ single-crystals. The thin film shows a high critical temperature ($T_c$) of 40.4 K with a sharp superconducting transition width of 0.2 K, and a high residual resistivity ratio (RRR=21), it reflects that $MgB_2$ thin film has a pure phase structure.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.364.1-364.1
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• 2016

We report the characteristics of individual ultra-long SnO2 nanowires(NWs) grown on sapphire(0001) substrates by vapor transport method. NWs, with typical lengths of >$400{\mu}m$, grew in the form of NW bundles under a hydrogen reducing atmosphere, without metal catalysts. The individual NWs were examined using high-resolution X-ray diffraction, transmission electron microscopy, and micro-Raman spectroscopy. The results revealed that the SnO2 NWs grew as high-quality, tetragonal-rutile-phase single crystals with mosaic distributions of $0.02^{\circ}$ and $0.026^{\circ}$ in the (101) and (110) planes, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.842-848
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• 2013

Developments of Solid-State Gyroscopy during last decades are impressive and were based on thin-walled shell resonators like HRG or CRG made from fused quartz or leuko-sapphire. However, a number of design choices for inertial-grade gyroscopes, which can be used for high-g applications and for mass- or middle-scale production, is still very limited. So, considerations of fundamental physical effects in solids that can be used for development of a miniature, completely solid-state, and lower-cost sensor look urgent. There is a variety of different types of bulk acoustic (elastic) waves (BAW) in anisotropic solids. Shear waves with different variants of their polarization have to be studied especially carefully, because shear sounds in glasses and crystals are sensitive to a turn of the solid as a whole, and, so, they can be used for development of gyroscopic sensors. For an isotropic medium (for a glass or a fine polycrystalline body), classic Lame's theorem (so-called, a general solution of Elasticity Theory or Green-Lame's representation) has been modified for enough general case: an elastic medium rotated about an arbitrary set of axes. Travelling, standing, and mixed shear waves propagating in an infinite isotopic medium (or between a pair of parallel reflecting surfaces) have been considered too. An analogy with classic Foucault's pendulum has been underlined for the effect of a turn of a polarizational plane (i.e., an integration effect for an input angular rate) due to a medium's turn about the axis of the wave propagation. These cases demonstrate a whole-angle regime of gyroscopic operation. Single-crystals are anisotropic media, and, therefore, to reflect influence of the crystal's rotation, classic Christoffel-Green's tensors have been modified. Cases of acoustic axes corresponding to equal velocities for a pair of the pure-transverse (shear) waves have of an evident applied interest. For such a special direction in a crystal, different polarizations of waves are possible, and the gyroscopic effect of "polarizational precession" can be observed like for a glass. Naturally, formation of a wave pattern in a massive elastic body is much more complex due to reflections from its boundaries. Some of these complexities can be eliminated. However, a non-homogeneity has a fundamental nature for any amorphous medium due to its thermodynamically-unstable micro-structure, having fluctuations of the rapidly-frozen liquid. For single-crystalline structures, blockness (walls of dislocations) plays a similar role. Physical nature and kinematic particularities of several typical "drifts" in polarizational BAW gyros (P-BAW) have been considered briefly too. They include irregular precessions ("polarizational beats") due to: non-homogeneity of mass density and elastic moduli, dissymmetry of intrinsic losses, and an angular mismatch between propagation and acoustic axes.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.551-556
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• 2013

AlN films with c-axis orientation and thermal conductivity characteristics were deposited by using Pulsed Laser Deposition and the films were characterized by changing the deposition conditions. In particular, we investigated the optimal conditions for the application of a heat sinking plane AlN thin film. Epitaxial AlN films were deposited on sapphire ($c-Al_2O_3$) single crystals by pulsed laser deposition (PLD) with an AlN target. AlN films were deposited at a fixed pressure of $2{\times}10^{-5}$ Torr, while the substrate temperature was varied from 500 to $700^{\circ}C$. According to the experimental results of the growth temperature of the thin film, AlN thin films were confirmed with a highly c-axis orientation, maximum grain size, and high thermal conductivity at $650^{\circ}C$. The thermal conductivity of the AlN thin film was found to increase compared to bulk AlN near the band gap value of 6.2 eV.

• Transactions of Materials Processing
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• v.29 no.1
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• pp.44-48
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• 2020

Aluminum nitride (AlN), as a substrate material in electronic packaging, has attracted considerable attention over the last few decades because of its excellent properties, which include high thermal conductivity, a coefficient of thermal expansion that matches well with that of silicon, and a moderately low dielectric constant. AlN films with c-axis orientation and thermal conductivity characteristics were deposited by using Pulsed Laser Deposition (PLD). The epitaxial AlN films were grown on sapphire (c-Al₂O₃) single crystals by PLD with AlN target and Y₂O₃ doped AlN target. A comparison of different targets associated with AlN films deposited by PLD was presented with particular emphasis on thermal conductivity properties. The quality of AlN films was found to strongly depend on the growth temperature that was exerted during deposition. AlN thin films deposited using Y₂O₃-AlN targets doped with sintering additives showed relatively higher thermal conductivity than while using pure AlN targets. AlN thin films deposited at 600℃ were confirmed to have highly c-axis orientation and thermal conductivity of 39.413 W/mK.

• Journal of Sensor Science and Technology
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• v.13 no.5
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• pp.399-404
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• 2004

We report on the technology of formation of sandwich structures based on fullerite films and on experimental results in research of optical and conductivity properties of these sandwich samples. Single crystals of sapphire (100) or silicon were used as substrates. The sandwich specimens were based on the structure M/$C_{60}$/M (M=Cr, Pd, Ag, Al, Cu). The thickness of the fullerite films was about $0.2{\sim}1.0{\mu}m$. The area of the $C_{60}$ film under the top contact was about $1cm^{2}$. The specimens have been investigated by infrared spectroscopy, spectra-photometry, ellipsometry and X-ray diffraction analysis. Measurements of the current/voltage characteristics and research on the temperature dependence of conductivity were performed as well. It was shown that metals such as Cr, Pd, Ag, Al, and Cu penetrate easily into the fullerite films. It appears that these specimens have a large conductivity. For silver/$C_{60}$ and other sandwich structures the conductivities show a semiconductor-like behaviour.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.315.2-315.2
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• 2014

Pt-functionalized ZnS nanowires were synthesized on Au-deposited c-plane sapphire substrates by thermal evaporation of ZnS powders followed by wet Pt coating and annealing. The $NO_2$ gas sensing properties of multiple-networked Pt-functionalized ZnS nanowire sensors were examined. Scanning electron microscopy showed the nanowires with diameters of 20-80 nm. Transmission electron microscopy and X-ray diffraction showed that the nanowires were wurtzite-structured ZnS single crystals. The Pt-functionalized ZnS nanowire sensors showed enhanced sensing performance to $NO_2$ gas at $150^{\circ}C$ compared to pristine ZnS nanowire sensors. Pristine and Pt-functionalized ZnS nanowire sensors showed responses of 140-211% and 207-488%, respectively, to 1-5 ppm $NO_2$, which are better than or comparable to those of many oxide semiconductor sensors. In addition, the underlying mechanism of the enhancement of the sensing properties of ZnS nanowires by Pt functionalization is discussed.