• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.1
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• pp.7-13
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• 2010

We have investigated effects of the rapid thermal annealing of GaN epilayers by molecular beam epitaxy in nitrogen atmosphere. The improvement of structural properties of the samples was observed after rapid thermal annealing under optimum conditions. This improvement in crystal quality is due to a reduction of the spread in the lattice parameter in epilayers. The annealing has been performed in a rapid thermal annealing furnace at $950^{\circ}C$. The effect of rapid thermal annealing on the structural properties of GaN was studied by x-ray diffraction. The Bragg peak shifts toward larger angle as the annealing time increases. As the thermal treatment time increases, FWHM(full width at half maximum) of the peak slightly increase with its decreases followed and it increases again. Results demonstrate that rapid thermal annealing did not always promote qualities of GaN epilayers. However, rapid thermal annealing under optimum conditions improve structural properties of the samples, elevating their crystal quality with a reduction of inaccuracy in the lattice parameter of the epilayers.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.51-51
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• 2011

We have grown nanocrystalline graphite on sapphire substrate by using solid carbon source molecular beam epitaxy. Changes of structure from amorphous carbon to nanocrystalline graphite controlled by the growth temperature have been investigated by Raman spectroscopy. Raman spectra show D, G, and 2D peaks, whose intensities vary on the growth temperature. Atomic force microscopy reveals that the surface is very flat. Sapphire substrates of different cutting direction produce similar results. Simulations suggest that the interaction between carbon and oxygen causes disorders. Electrical transport measurements exhibit a Dirac-like peak, including a carrier type change by an external gate voltage bias.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.155-156
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• 2006

Single crystalline ZnO fims were successfully grown on r-plane sapphire substrate by plasma-assisted molecular beam epitaxy. Epitaxial relationship between the ZnO film and the-r-plane sapphire was determined to be [-1101]$Al_2O_3\;{\parallel}$ [0001]ZnO, [11-20]$Al_2O_3\;{\parallel}$ [-1100]ZnO based on the in-situ RHEED analysis and confirmed again by HRXRD measurements. Grown (11-20) ZnO films showed faceted structure along the <0001> direction and the RMS roughness was about 4 nm.

• Journal of IKEEE
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• v.13 no.4
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• pp.23-27
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• 2009

Ohmic contact formation and etching processes for the fabrication of MBE (molecular beam epitaxy) grown GaSb-based p-channel HEMT devices on Si substrate have been studied. Firstly, mesa etching process was established for device isolation, based on both HF-based wet etching and ICP-based dry etching. Ohmic contact process for the source and drain formation was also studied based on Ge/Au/Ni/Au metal stack, which resulted in a contact resistance as low as $0.683\;{\Omega}mm$ with RTA at $320^{\circ}C$ for 60s. Finally, for gate formation of HEMT device, gate recess process was studied based on AZ300 developer and citric acid-based wet etching, in which the latter turned out to have high etching selectivity between GaSb and AlGaSb layers that were used as the cap and the barrier of the device, respectively.

• Journal of Sensor Science and Technology
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• v.15 no.3
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• pp.216-221
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• 2006

ZnO thin films prepared by PLD method exhibit an excellent optical property, but may have some problems such as incomplete surface roughness and crystallinity. In this study, undoped ZnO buffer layers were deposited on (0001) sapphire substrates by ultra high vacuum pulse laser deposition (UHV-PLD) and molecular beam epitaxy (MBE) methods, respectively. After post annealing of ZnO buffer layer, undoped ZnO thin films were deposited under different oxygen pressure ($35{\sim}350$ mtorr) conditions. The Arsenic-doped (1, 3 wt%) ZnO thin layers were deposited on the buffer layer of undoped ZnO by UHV-PLD method. The optical property of the ZnO thin films was analyzed by photoluminescence (PL) measurement. The ${\theta}-2{\theta}$ XRD analysis exhibited a strong (002)-peak, which indicates c-axis preferred orientation. Field emission-scanning electron microscope (FE-SEM) revealed that microstructures of the ZnO thin films were varied by oxygen partial pressure, Arsenic doping concentration, and deposition method of the undoped ZnO buffer layer. The denser and smoother films were obtained when employing MBE-buffer layer under lower oxygen partial pressure. It was also found that higher Arsenic concentration gave the enhanced growing of columnar structure of the ZnO thin films.

• Journal of the Korean Vacuum Society
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• v.7 no.4
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• pp.334-340
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• 1998

Photoreflectance (PR) measurents have been performed on $In_xGa_{1-x}As/GaAs$ grown by molecular beam epitaxy (MBE). Bandgap $(E_0)$ of $In_xGa_{1-x}As$ epilayer measured from PR was separated as heavy-hole $(E_0(HH))$ and light-hole $(E_0(LH))$ by strain effect. The compositions and the strains of epilayer were obtained from the energy value of $E_0(HH)$ and from energy difference of $E_0(HH)$ and $E_0(LH)$, respectively. In addition, the PR signal of $E_0(LH)$ was diminished below 160 K. The interface electric field (E) of InGaAs/GaAs was increased from $0.75{\times}10^5$ V/cm to $2.66{\times}10^5$ V/cm as In composition increased, which was calculated from Franz-Keldysh oscillation (FKO) peaks. As the temperature dependence of the PR signal at x=0.09 sample, we obtained Varshni and Bose-Einstein coefficients.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.203.1-203.1
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• 2013

Zinc oxide (ZnO) nanocrystalline thin films on various growth temperatures for active layer and different buffer layer thickness were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on Si substrates. The ZnO active layer were grown with various growth temperature from 500 to $800^{\circ}C$ and the ZnO buffer layer were grown for different time from 5 to 40 minutes. To investigate the structural and optical properties of the ZnO thin films, scanning electron microscope (SEM), X-ray diffractometer (XRD), and photoluminescence (PL) spectroscopy were used, respectively. In the SEM images, the ZnO thin films have high densification of grains and good roughness and uniformity at $800^{\circ}C$ for active layer growth temperature and 20 minutes for buffer layer growth time, respectively. The PL spectra of ZnO buffer layers and active layers display sharp near band edge (NBE) emissions in UV range and broad deep level emissions (DLE) in visible range. The intensity of NBE peaks for the ZnO thin films significantly increase with increase in the active layer growth temperature. In addition, the NBE peak at 20 minutes for buffer layer growth time has the largest emission intensity and the intensity of DLE peaks decrease with increase in the growth time.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.6
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• pp.446-450
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• 2013

Growth mechanism of GS-MBE(Gas source-Molecular Beam Epitaxy) has been investigated. We observed that the growth rate of GaN films is changing from 520 nm/h to 440 nm/h by the variation of V/III ratio under nitrogen-rich growth condition. It was explained that the amount of hydrogen on the growth front varies by the ammonia flow, and gallium hydrides are generated on the surface by a reaction of hydrogen and gallium, resultantly the amount of gallium supplying is changing along with the $NH_3$ flow. Reflection high energy electron diffraction (RHEED) observation was used to confirm the N-rich condition. The crystal quality of GaN was estimated by photoluminescence (PL) and X-ray diffraction (XRD).

• Journal of the Korean Society for Heat Treatment
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• v.31 no.5
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• pp.237-243
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• 2018

In-rich InGaN epilayers were grown on (0001) sapphire substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). InGaN epilayers grown at various growth condition were observed by SEM, XRD, and RHEED. When plasma power of nitrogen increased from 290 to 350 W, surface morphology and crystal quality became worse according to more active nitrogen on the surface of InGaN at N-rich growth condition. As In composition was reduced from 89 to 71% by changing the incoming flux of In and Ga, surface morphology and crystal quality became worse. In addition, weak peaks of cubic InGaN phase was observed from InGaN layer with 71% In composition by XRD ${\Phi}$ scan measurement. When growth temperature decreased from 500 to $400^{\circ}C$, RHEED diffraction pattern was changed to be from streaky to spotty which means atomically rough surface, and spotty pattern showed cubic symmetry of InGaN clearly. XRD ${\Phi}$ scan measurement gave clear evidence that more cubic InGaN phase was formed at low growth temperature. All these results indicates that extremely low surface mobility of Ga adatom caused inferior crystal quality and cubic InGaN phase.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.12
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• pp.142-148
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• 1995

Sb ${\delta}$-doped Si layers were grown by Si MBE (Molecular Beam Epitaxy) system using substrate temperature modulation technique. The Si substrate temperatures were modulated between 350$^{\circ}C$ and 600$^{\circ}C$. The doping profile was as narrow as 41$\AA$ and the doping concentration of up to 3.5${\times}10^{20}cm^{3}$ was obtained. The film quality was as good as bulk material as verified by RHEED (Reflected High Energy Electron Diffraction), SRP (Spreading Resistance Profiling) and Hall measurement. Since the film quality is not degraded after the growth a Sb ${\delta}$-doped Si layer, the ${\delta}$-doped layers can be repeated as many times as we want. The doping technique is useful for many Si devices including small scale devices and those which utilize quantum mechanical effects.