• Korean Journal of Materials Research
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• v.10 no.4
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• pp.276-281
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• 2000

Silicon carbide(SiC) films were grown on modified Si(111) surface with a SiNx in the NH$_3$surrounding. Thickness of SiC films was decreased with increasing of the nitridation time. Also, voids having crystal defects were removed at interface of SiC/Si according to growth parameters. SiC films were grown on SiNx/Si substrate of 100, 300 and 500nm thickness. SiC films were deposited along [111] direction and columnar grains of SiC crystal. The void-free film was observed in the interface of SiC/SiNx. This result suggests that fabrication of SiC devices are applied to SiNx replacing silicon oxide in SOI structure.

• Korean Journal of Materials Research
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• v.24 no.4
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• pp.194-200
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• 2014

Metallic Cr film coatings of $1.2{\mu}m$ thickness were prepared by DC magnetron sputter deposition method on c-plane sapphire substrates. The thin Cr films were ammoniated during horizontal furnace thermal annealing for 10-240 min in $NH_3$ gas flow conditions between 400 and $900^{\circ}C$. After annealing, changes in the crystal phase and chemical constituents of the films were characterized using X-ray diffraction (XRD) and energy dispersive X-ray photoelectron spectroscopy (XPS) surface analysis. Nitridation of the metallic Cr films begins at $500^{\circ}C$ and with further increases in annealing temperature not only chromium nitrides ($Cr_2N$ and CrN) but also chromium oxide ($Cr_2O_3$) was detected. The oxygen in the films originated from contamination during the film formation. With further increase of temperature above $800^{\circ}C$, the nitrogen species were sufficiently supplied to the film's surface and transformed to the single-phase of CrN. However, the CrN phase was only available in a very small process window owing to the oxygen contamination during the sputter deposition. From the XPS analysis, the atomic concentration of oxygen in the as-deposited film was about 40 at% and decreased to the value of 15 at% with increase in annealing temperature up to $900^{\circ}C$, while the nitrogen concentration was increased to 42 at%.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.771-782
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• 1989

Synthesis of $\beta$-Sialon powder was attempted with carbothermal reduction of porous glass. The porous glass was prepared by heat and hydrothermal treatments of 9.32 Li2O.46.5B2O3.37.2SiO2.6.98Al2O3 glass. Carbon pyrolyzed from propane gas was deposited on the porous glass, thereafter activated carbon was added as reducing agents. The synthesized $\beta$-Sialon powder was pressureless sintered at 175$0^{\circ}C$ for 1hr in N2 atmosphere. The characterization of the $\beta$-Sialon powder was performed with XRD, BET, SEM and particle size analysis. The sinterability and mechanical properties of the sintered bodies were investigated in terms of bulk density, M.O.R., fracture toughness, morphology of microstructure and etc. The reduction effect of deposited carbon was better than that of activated carbon mechanically added. The formation of SiC was precominant over that of Si2ON2 and $\beta$-Sialon owing to low partial pressure of N2 inside the pore, wehreas on the surface of porous glass the formation of Si2ON2 and $\beta$-Sialon were predominant. Thereafter, SiC reduced unreacted glass to be $\beta$-Sialon. Single phase of $\beta$-Sialon(Z=1.92) was obtained from PGA porous glass having the largest pore radius by the simultaneous reduction and nitridation method at 145$0^{\circ}C$ for 5hrs. The bulk density, M.O.R., and KIC of the sitered body are 3.17g/cc, 434.4MPa and 4.1MPa.m1/2, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.99-99
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• 2008

To grow the large diameter GaN with high structure and optical quality has been obtained by hydride vapor phase epitaxy(HVPE) method. In addition to the nitridation of $Al_2O_3$ substrate, we also developed a "step-growth process" to reduce or to eliminate the bowing of the GaN substrate caused by thermal mismatch during cool down after growth. The as-grown 380um thickness and 75mm diameter GaN layer was separated from the sapphire substrate by laser-induced lift-off process at $600^{\circ}C$. A problem with the free-standing wafer is the typically large bowing of such a wafer, due to the built in the defect concentration near GaN-sapphire interface. A polished G-surface of the GaN substrate were characterized by room temperature Double crystal X-ray diffraction (DCXRD), photoluminescence(PL) measurement, giving rise to the full-width at half maximum(FWHM) of the rocking curve of about 107 arcsec and dislocation density of $6.2\times10^6/cm^2$.

• Journal of Powder Materials
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• v.19 no.1
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• pp.25-31
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• 2012

In this study, a high energy ball milling process was employed in order to improve the densification of direct nitrided AlN powder. The densification behavior and the sintered microstructure of the milled AlN powder were investigated. Mixture of AlN powder doped with 5 wt.% $Y_2O_3$ as a sintering additive was pulverized and dispersed up to 50 min in a bead mill with very small $ZrO_2$ beads. Ultrafine AlN powder with a particle size of 600 nm and a specific surface area of 9.54 $m^2/g$ was prepared after milling for 50 min. The milled powders were pressureless-sintered at $1700^{\circ}C-1800^{\circ}C$ for 4 h under $N_2$ atmosphere. This powder showed excellent sinterability leading to full densification after sintering at $1700^{\circ}C$ for 4 h. However, the sintered microstructure revealed that the fraction of yitttium aluminate increased with milling time and sintering temperature and the newly-secondary phase of ZrN was observed due to the reaction of AlN with the $ZrO_2$ impurity.

• Applied Microscopy
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• v.30 no.4
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• pp.337-345
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• 2000

Introduction of the buffer layer and the nitridation of a sapphire substrate were one of the most general methods employed for the reduction of lattice defects in GaN thin films Brown on sapphire by MOCVD. In an effort to improve the initial nucleation and growth condition of the GaN, reactive ion beam (RIB) of nitrogen treatment of the sapphire surface has been attempted. The 10 nm thick, amorphous $AlO_xN_y$ layer was formed by RIB and was partially crystallized alter the main growth of GaN at high temperature, leaving isolated amorphous regions at the interface. The beneficial effect of amorphous layer at interface in relieving the thermal stress between substrate and GaN film was examined by measuring the lattice strain value of the GaN film grown with and without the RIB treatment. Higher order Laue zone pattern (HOLZ) of $[\bar{2}201]$ zone axis was compared with simulated patterns and lattice strain was estimated It was confirmed that the great reduction of thermal strain was achieved by RIB process and the amount of thermal stress was 6 times higher in the GaN film grown by conventional method without the RIB treatment.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.634-638
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• 2011

We report growth of epitaxial AlN thin films on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. To achieve two-dimensional growth the substrates were nitrided by nitrogen plasma prior to the AlN growth, which resulted in the formation of a two-dimensional single crystalline AlN layer. The formation of the two-dimensional AlN layer by the nitridation process was confirmed by the observation of streaky reflection high energy electron diffraction (RHEED) patterns. The growth of AlN thin films was performed on the nitrided AlN layer by changing the Al beam flux with the fixed nitrogen flux at 860$^{\circ}C$. The growth mode of AlN films was also affected by the beam flux. By increasing the Al beam flux, two-dimensional growth of AlN films was favored, and a very flat surface with a root mean square roughness of 0.196 nm (for the 2 ${\mu}m$ ${\times}$ 2 ${\mu}m$ area) was obtained. Interestingly, additional diffraction lines were observed for the two-dimensionally grown AlN films, which were probably caused by the Al adlayer, which was similar to a report of Ga adlayer in the two-dimensional growth of GaN. Al droplets were observed in the sample grown with a higher Al beam flux after cooling to room temperature, which resulted from the excessive Al flux.