• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.74-75
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• 2005

ZnO epilayer were synthesized by the pulesd laser deposition(PLD) process on $Al_2O_3$ substrate after irradiating the surface of the ZnO sintered pellet by the ArF(193 nm) excimer laser. The epilayers of ZnO were achieved on sapphire ($Al_2O_3$) substrate at a temperature of $400^{\circ}C$. The crystalline structure of epilayer was investigated by the photoluminescence. The carrier density and mobility of ZnO epilayer measured with Hall effect by van der Pauw method are $8.27{\times}10^{16}cm^{-3}$ and $299cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the ZnO obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T) = 3.3973 eV - ($2.69{\times}10^{-4}$ eV/K)$T_2$/(T + 463 K). The crystal field and the spin-orbit splitting energies for the valence band of the ZnO have been estimated to be 0.0041 eV and 0.0399 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the $\triangle$so definitely exists in the $\ulcorner_6$ states of the valence band of the ZnO. The three photocurrent peaks observed at 10K are ascribed to the $A_1-$, $B_1-$, and $C_1$-exciton peaks for n = 1.

• 센서학회지
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• 제14권3호
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• pp.160-168
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• 2005

ZnO epilayer were synthesized by the pulesd laser deposition(PLD) process on $Al_{2}O_{3}$ substrate after irradiating the surface of the ZnO sintered pellet by the ArF(193 nm) excimer laser. The epilayers of ZnO were achieved on sapphire ($Al_{2}O_{3}$) substrate at a temperature of $400^{\circ}C$. The crystalline structure of epilayer was investigated by the photoluminescence. The carrier density and mobility of ZnO epilayer measured with Hall effect by van der Pauw method are $8.27{\times}1016cm^{-3}$ and $299cm^{2}/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the ZnO obtained from the absorption spectra was well described by the Varshni's relation, $E_{g}(T)$=3.3973 eV-($2.69{\times}10^{-4}$ eV/K)$T^{2}$/(T+463K). The crystal field and the spin-orbit splitting energies for the valence band of the ZnO have been estimated to be 0.0041 eV and 0.0399 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the ${\Gamma}_{6}$ states of the valence band of the ZnO. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1}-$, $B_{1}-$, and $C_{1}-$exciton peaks for n = 1.

• 한국자기학회지
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• 제21권3호
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• pp.88-92
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• 2011

Pulsed Laser Deposition 방법을 사용하여 $Zn_{0.4}Fe_{2.6}O_4$ 박막을 증착하였으며 이의 결정성 및 자기적 특성을 증착온도의 함수로 조사하였다. 증착온도가 $300^{\circ}C$었을 경우 박막은 코런돔(corundom) ${\alpha}-$Fe_2O_3$ 또는 워자이트(wurzite) ZnO 구조를 지니고 있었으나 증착온도가 $500^{\circ}C$로 증가되었을 경우에는 $Zn_{0.4}Fe_{2.6}O_4(111)/Al_2O_3(0001)$의 결정 방향을 지닌 매우 안정된 역스피넬(inverse spinel) 성장이 이루어졌으며 또한 표면의 거칠기도 증착온도가 $300^{\circ}C$ 일 때 보다 더 평평하여졌다. 이러한 역스피넬 $Zn_{0.4}Fe_{2.6_O_4$ 박막에서는 X-선 산란 분석 결과 ${\alpha}-$Fe_2O_3$, ZnO에 해당하는 픽들은 전혀 관측되지 않았으며 이러한 사실들은 Zn가 증착온도를 높여줌에 따라 역스피넬의 사면체 자리에 치환되었음을 의미한다. M-H 곡선의 측정 결과 증착온도 $300^{\circ}C$ 박막은 자성 특성이 거의 관측되지 않은 반면 $500^{\circ}C$ 박막의 경우에는 매우 뚜렷한 강자성 특성을 확인할 수 있었으며 벌크보다 작은 포화자화 값은 팔면체 자리의 Fe 스핀들의 삐뚤림(canting)에 의한 것으로 이해된다.

• 한국결정성장학회지
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• 제6권2호
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• pp.238-246
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• 1996

$\beta$-SiC와 AIN의 혼합분말로부터 열간가압소결에 의하여 고밀도의 SiC-AIN 고용체가 $1870^{\circ}C$에서 $2030^{\circ}C$ 사이의 온도범위에서 제조되어졌다. 온도와 SiC/AIN의 비 및 seed의 존재에 따라 AIN과 $\beta$-SiC(3C) 분말의 반응은 2 H (wurzite) 구조로의 전이를 나타내었다. 결정상들은 SiC-rich 및 AIN-rich 고용체로 구성되었다. $2030^{\circ}C$, 1시간에서 5 wt%의 $\alpha$-SiC seed를 첨가한 50 % AIN/50% SiC의 조성에 대하여 완전한 고용체가 얻어졌으며, 미세구조가 비교적 균일한 2 H상의 결정립 크기를 가지고균일한 성장경향을 나타내었다. SiC-AIN 고용체에 있어서 $\alpha$-SiC seed의 변수가 전이기구 및 결정립의 크기와 모양을 비롯한 결정립 크기의 분포, 조성의 불균일성과 구조적 결함 등에 영향을 미칠 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.290.2-290.2
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• 2016

Recently, organic thin-film transistors have been widely researched for organic light-emitting diode panels, memory devices, logic circuits for flexible display because of its virtue of mechanical flexibility, low fabrication cost, low process temperature, and large area production. In order to achieve high performance OTFTs, increase in accumulation carrier mobility is a critical factor. Post-fabrication thermal annealing process has been known as one of the methods to achieve this by improving the crystal quality of organic semiconductor materials In this paper, we researched the properties of pentacene films with X-Ray Diffraction (XRD) and Atomic Force Microscope (AFM) analyses as different annealing temperature in N2 ambient. Electrical characterization of the pentacene based thin film transistor was also conducted by transfer length method (TLM) with different annealing temperature in Al- and Ti-pentacene junctions to confirm the Fermi level pinning phenomenon. For Al- and Ti-pentacene junctions, is was found that as the surface quality of the pentacene films changed as annealing temperature increased, the hole-barrier height (h-BH) that were controlled by Fermi level pinning were effectively reduced.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권5호
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• pp.242-242
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• 2004

The composites were fabricated 61 vol.%α-α-SiC and 39vol.% WC powders with the liquid forming additives of 12wt% Al₂O₃＋Y₂O₃ by pressureless annealing at 1700, 1800, 1900℃ for 4 hours. The result of phase analysis of composites by XRD revealed α-SiC(2H), WC, and YAG($Al_5Y_3O_{12}$) crystal phase. The relative density, the flexural strength, fracture toughness and Young′s modulus showed respectively the highest value of 99.4%, 375.76㎫, 5.79㎫ㆍ$m^{\frac{1}{2}}$, and 106.43㎬ for composite by pressureless annealing temperature 1900℃ at room temperature. The electrical resistivity showed the lowest value of 1.47×$10^{-3}$/Ω·㎝ for composite by pressureless annealing temperature 1900℃ at 25℃. The electrical resistivity of the α-SiC-WC composites was all positive temperature cofficient resistance (PTCR) in the temperature ranges from 25℃ to 500℃.

• 분석과학
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• 제21권3호
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• pp.229-236
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• 2008

본 연구에서 HCl을 처리하지 않고 혹은 HCl 처리한 표면 처리된 MWCNT 및 TNB를 이용하여 $C/TiO_2$ 복합체를 제조하였다. XRD 결과 값으로부터 모두 시료에 한 가지 결정 구조 즉 anatase형을 존재하고 있음을 알 수 있었다. SEM 사진으로부터 $TiO_2$ 입자와 CNT는 균일하게 분포하고 있음을 알 수 있었다. EDX 결과에서, 모두 시료에 C, O, Al와 Ti 피크를 볼 수 있으며, 특히 시료 CT에 있는 C와 Ti의 함량은 시료 HCT에 있는 것보다 많게 나타났다. 마지막으로, $C/TiO_2$ 복합체는 $TiO_2$보다 더 좋은 광촉매 특성을 가지고 있음을 알 수 있었다.

• 한국재료학회지
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• 제20권1호
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• pp.47-50
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• 2010

Various thicknesses of Al-doped ZnO (AZO) films were deposited on glass substrate using pulsed dc magnetron sputtering with a cylindrical target designed for large-area high-speed deposition. The structural, electrical, and optical properties of the films of various thicknesses were characterized. All deposited AZO films have (0002) preferred orientation with the c-axis perpendicular to the substrate. Crystal quality and surface morphology of the films changed according to the film thickness. The samples with higher surface roughness exhibited lower Hall mobility. Analysis of the measured data of the optical band gap and the carrier concentration revealed that there were no changes for all the film thicknesses. The optical transmittances were more than 85% regardless of film thickness within the visible wavelength region. The lowest resistivity, $4.13\times10^{-4}\Omega{\cdot}cm^{-1}$ was found in 750 nm films with an electron mobility $(\mu)$ of $10.6 cm^2V^{-1} s^{-1}$ and a carrier concentration (n) of $1.42\times10^{21} cm^{-3}$.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.232-232
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• 2010

Recently light emitting diodes (LEDs) have been expected as the new generation light sources because of their advantages such as small size, long lifetime and energy-saving. GaN, as a wide band gap material, is widely used as a material of LEDs and GaN nanorods are the one of the most widely investigated nanostructure which has advantages for the light extraction of LEDs and increasing the active area by making the cylindrical core-shell structure. Lately GaN nanorods are fabricated by various techniques, such as selective area growth, vapor-liquid-solid (VLS) technique. But these techniques have some disadvantages. Selective area growth technique is too complicated and expensive to grow the rods. And in the case of VLS technique, GaN nanorods are not vertically aligned well and the metal catalyst may act as the impurity. So we just tried to grow the GaN nanorods on Si substrate without catalyst to get the vertically well aligned nanorods without impurity. First we deposited the AlN buffer layer on Si substrate which shows more vertical growth mode than sapphire substrate. After the buffer growth, we flew trimethylgallium (TMGa) as the III group source and ammonia as the V group source. And during the GaN growth, we kept the ammonia flow stable and periodically changed the flow rate of TMGa to change the growth mode of the nanorods. Finally, as the optimization, we changed the various growth conditions such as the growth temperature, the working pressure, V/III ratio and the doping level. And we are still in the process to reduce the diameter of the nanorods and to extend the length of the nanorods simultaneously. In this study, we focused on the shape changing of GaN nanorods with different growth conditions. So we confirmed the shape of the nanorods by scanning electron microscope (SEM) and carried out the Photoluminescence (PL) measurement and x-ray diffraction (XRD) to examine the crystal quality difference between samples. Detailed results will be discussed.

• 한국결정성장학회지
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• 제7권3호
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• pp.428-436
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• 1997

0.8$\mu$의 평균입자크기와 63$m^2/g$의 비표면적을 갖는 소질성이 뛰어난 hexacelsian분말이 so;ution-polymerization 방법에 의해 제조되어졌다. polymerization 경정을 통한 분말합성을 위하여 PVA 용액이 사용되었다. 소결후 치밀화된 hexacelsian은 $\alpha$,$\beta$,$\gamma$ 간의 상전이 거동을 보였고, 상대밀도 98.5% 의 치밀화ㄱ된 celsian 소결체가 $1600^{\circ}C$에서 72시간의 서냉공정을 거쳐hexacelsian의 상전이에 의하여 얻어졌다.