• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.18 no.10
• /
• pp.2497-2502
• /
• 2014

The 5 wt.% Ga-doped zinc oxide (GZO) thin films were fabricated on PES substrates with various RF power 50~80 W by using RF magnetron sputtering in order to investigate the optical and electrical properties of GZO thin films. The XRD measurement showed that GZO thin films exhibit c-axis orientation. At a RF power of 70W, the GZO thin film showed the highest (002) diffraction peak with a Full-Width-Half-Maximum (FWHM) of $0.44^{\circ}$. AFM analysis showed that the lowest surface roughness (0.20 nm) was obtained for the GZO thin film fabricated at 70 W of RF power. The electrical property indicated that the minimum resistivity ($6.93{\times}10^{-4}{\Omega}{\cdot}cm$) and maximum carrier concentration ($7.04{\times}10^{20}cm^{-3}$) and hall mobility ($12.70cm^2/Vs$) were obtained in the GZO thin film fabricated at 70W of RF power. The optical transmittance in the visible region was higher than 80 %, regardless of RF power. The optical band-gap showed the slight blue-shift with increased in carrier concentration which can be explained by the Burstein-Moss effect.

• Journal of the Korean Applied Science and Technology
• /
• v.34 no.1
• /
• pp.50-57
• /
• 2017

Zinc oxide is, one of metal oxide semiconductor, harmless to human and environment-friendly. It has excellent chemical and thermal stability properties. Wurtzite-zinc oxide is a large band gap energy of 3.37 eV and high exciton binding energy of 60 meV. It can be applied to various fields, such as solar cells, degradation of the dye waste, the gas sensor. The photocatalytic activity of zinc oxide is varied according to the particle shape and change of crystallinity. Therefore, It is very important to specify the additives and the experimental variables. In this study, the zinc oxide were synthesized by using a microwave assisted hydrothermal synthesis. The precursor was used as the zinc nitrate, the pH value was controlled as 11 by NaOH. Surfactants are the ethanolamine, cetyltrimethylammonium bromide, sodium dodecyl sulfate, sorbitan monooleate was added by changing the concentration. The composite particles had the shape of a star-like, curcular cone, seed shape, flake-sphere. Physical and chemical properties of the obtained zinc oxide was characterized using x-ray diffractometer, field emission scanning electron microscopy, thermogravimetric analysis and optical properties was characterized using UV-visible spectroscopy, photoluminescence and raman spectroscopy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.20-20
• /
• 2008

최근 LEDs가 동일 효율의 전구에 비해 에너지 절감 효과 크며 신뢰성이 뛰어나다기 때문에 기존 광원을 빠르게 대체해 나가고 있다. 특히 자외선 파장을 가지는 LEDs는 발열이 낮아 냉각장치가 필요 없으며, 수명이 길어 기존 UV lamp에 비해 많은 장점을 가지고 있기 때문에 많은 관심을 밭고 있다. 그럼에도 불구하고 자외선 LEDs는 제조 단가가 높고 power가 낮아 소요량이 많은 등 아직 해결해야 할 부분이 많기 때문에 이를 해결하기 위해 여러가지 재료와 다양한 구조가 고려되고 있다. 그 중 ZnO는 II-VI족 화합물 반도체로써 UV영역의 넓은 밴드갭(3.37eV)을 가지는 투명한 재료이다. 특히 ZnO는 60meV의 큰 엑시톤 결합에너지를 가지며, 가시광 영역에서 높은 투과율을 가지고, 상온에서 물리적, 화학적으로 안정하기 때문에 UV sensor, UV laser, UV converter, UV LEDs 등 광소자 분야에서 연구가 활발히 진행되고 있다. ZnO가 광소자의 발광재료로써 높은 효율을 얻기 위해서는 결정성을 높여 내부 결함을 감소시키며, 발광 면적을 높일 수 있는 구조가 요구된다. 특히 MOCVD 법으로 성장한 나노막대는 에피성장되어 높은 결정성을 기대할 수 있으며, 성장 조건을 조절함으로써 나노막대의 aspect ratio와 밀도 제어할 수 있기 때문에 표면적을 효과적으로 넓혀 높은 발광효율을 얻을 수 있다. 본 실험에서는 MOCVD 법으로 실리콘과 사파이어 기판 위에 다양한 성장 온도를 가진 나노구조를 성장 시키고 온도에 따른 형상 변화와 특성을 평가하였다. ZnO 의 성장온도가 약 $360^{\circ}C$ 일 때, 밀도가 조밀하고 기판에 수직 배열한 균일한 나노막대가 성장되었으며 우수한 결정성, 광학적 특성이 나타남을 SEM, TEM, PL, XRD를 사용하여 확인하였다.

• Journal of the Korean Vacuum Society
• /
• v.8 no.1
• /
• pp.51-54
• /
• 1999

Hydrogenated amorphous silicon (a-Si:H) films are fabricated by Argon radical annealing (ArRA). The deposition rate of continuously deposited a-Si:H film is 1.9 $\AA$/s. As ArRA time are increased to 0.5 and 1 minute, the deposition rate are increased to 2.8 $\AA$/s and 3.3 $\\AA$/s. The deposition rate of a-si:H films with 2 and 3 minutes ArRA time are 3.3 $\AA$/s. As the ArRA time is increased, the optical band gap and the hydrogen contents in the a-Si:H films are increased and slightly decreased. The light-induced degradation of ArRA treated a-Si:H films are less than that of continuously deposited a-Si:H film. The dark conductivity and the conductivity activation energy ($E_a$) of continuously deposited a-Si:H film are decreased to 1/25 in room temperature and increased to 0.09eV By 1 hour light soaking, respectively. The dark conductivity and $E_a$ of ArRA treated a-Si:H film decreased to 1/3 in room temperature and increased to 0.03eV by 1 hour light soaking, respectively. We could improve the stability of a-Si:H films under the light soaking by ArRA technique and discussed the microscopic process of ArRA technique.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.24-24
• /
• 2010

Chalcopyrite $Cu(In,Ga)Se_2$ (CIGS) 화합물 반도체는 고효율 박막태양전지의 광 흡수층으로 사용되는 물질 중 가장 우수한 효율 (19.9%, NREL 2008)을 보유하고 있다. CIGS는 직접천이형 에너지밴드갭 (direct bandgap)을 가지고 있고, 광흡수계수가 $1{\times}10^5\;cm^{-1}$로서 반도체 중 서 가장 흡수율이 높은 재료에 속하여 두께 $1{\sim}2\;{\mu}m$의 박막으로도 고효율의 태양전지 제조가 가능하고, 또한 장기적으로 전기광학적 안정성이 매우 우수한 특성을 지니고 있다. 현재 고효율 CIGS 셀생성을 위해 널리 사용되고 있는 CIGS 흡수층 성장공정은 "co-evaporation(동시증발법)"과 2-step 공정이라 불리는 "sputter-selenization(스퍼터-셀렌화)" 방법이다. 동시증발법은 개별원소 Cu, In, Ga, Se 들을 고진공 분위기에서 고온 ($550{\sim}600^{\circ}C$)기판위에 증착하는 방법으로 소면적에서 가장 좋은 효율(~20%)을 보이는 공정이다. 하지만, 고온, 고진공 공정조건과 대면적 증착시 온도 및 조성 불균일 등의 문제점 등으로 상용화에 어려움이 있다. 스퍼터-셀렌화 공정은 1단계에서 스퍼터링 방식으로 CuGaIn 전구체를 증착하고, 2단계에서 고온($550{\sim}600^{\circ}C$)하에 $H_2Se$ 혹은 Se vapor와 반응시켜 CIGS를 생성한다. 일본의 Showa Shell와 Honda Soltec 등에 의해 이미 상업화 되었듯이, 저비용 대면적으로 상업화 가능성이 높은 공정으로 평가되고 있다. 하지만, 2단계에서 사용되는 $H_2Se$ 및 Se vapor의 유독성, 기상 Se과 금속전구체 간의 느린 셀렌화 반응속도, 셀렌화반응 후 생성된 CIGS 박막 두께방향으로의 Ga 불균일분포, 생성된 CIGS/Mo 계면 접착력 저하등의 문제점들이 해결되어야만 상업화에 성공할 수 있을 것이다. 본 Tutorial에서는 CIGS 물질의 열역학 상평형과 반응메카니즘에 대해 설명하고, 다양한 생성 공정들을 소개할 것이다.

• Korean Journal of Optics and Photonics
• /
• v.9 no.4
• /
• pp.221-226
• /
• 1998

Ternary heavy metal oxide glasses in the $PbO-Bi_2O_3-Ga_2O_3$ system doped with $Er_2O_3$ were prepared and their spectroscopic properties, such as radiative transition probability, calculated and measured radiative lifetimes and cross-sections of 1.5 $\mu\textrm{m}$ and 2.7 $\mu\textrm{m}$ emissions were analyzed. Enhanced quantum efficiencies of some electronic transitions were evident mainly because of the low vibrational phonon energy ($~500cm^{-1}$) inherent in the host glasses. This seems to be the main reason for obtaining the 2.7 $\mu\textrm{m}$ luminescence which is normally quenched in the conventional oxide glasses. In addition, green and red fluorescence emissions were observed through the frequency upconversion processes of the 798 nm excitation. Non-radiative transition due to the multiphonon relaxation is a dominant lifetime-shortening mechanism in the 4f-4f transitions in $Er^{3+}$ ion except for the $^4S_{3/2}{\rightarrow}^4I_{15/2}$ transition where a non-radiative transfer to band-gap excitation of the host glasses is dominant. Melting of glasses under an inert gas atmosphere and (or) addition of the typical glass-network former into glasses is necessary in order to enhance the quantum efficiency of the transition.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2018.06a
• /
• pp.87-87
• /
• 2018

다이아몬드 상 탄소(diamond-like carbon, DLC)는 상당량의 $sp^3$ 결합을 가지는 비정질 탄소(a-C) 또는 수소화 비정질 탄소(a-C:H)로 이루어진 준안정 형태의 탄소이다. DLC는 전기 저항과 굴절률이 높고 화학적으로 다른 물질과 반응하지 않으며, 마찰계수가 낮고 경도가 높아 자기 디스크, 광학 소자 등의 다양한 분야에서 적용되고 있다[1,2]. 또한 다이아몬드에 비해 상온에서 성장이 가능할 정도로 합성온도가 낮아 적용 기판의 제한이 거의 없고, 증착 방법과 조건에 따라 탄소 결합의 다양성과 비정질성이 변화하기 때문에 넓은 범위의 특성을 얻을 수 있는 장점이 있다. 지금까지 DLC 박막의 광학적 특성, 특히 굴절률, 광학적인 에너지 밴드 갭, 자외선과 적외선 투과성에 대해서는 많은 연구가 진행되었으나 가시광선의 투과성에 대한 연구는 제한적이며[4], 가시광선 투과도 개선에 대한 연구는 전무하다. 본 연구에서는 ITO 기판 위에 DLC를 합성하고 기계적 특성과 가시광선 영역 투과도를 조사하였다. RF-PECVD(radio frequency plasma enhanced chemical vapor deposition) 방법에 의해서 $C_2H_2+Ar$ 혼합 가스 비율과 $C_2H_2+N_2$ 혼합 가스 비율을 변화시켜 ITO 기판 위에 DLC 박막을 합성하였다. 공정 압력과 rf-power, 증착시간, 기판온도는 0.2 torr, 40 W, 5 분, $50^{\circ}C$로 고정하고, 공정 가스는 $C_2H_2+Ar$과 $C_2H_2+N_2$가 200 sccm이 되도록 비율을 변화하였다. $C_2H_2:Ar$과 $C_2H_2:N_2$의 비율은 180 : 20, 160 : 40, 140 : 60, 120 : 80, 100 : 100이 되도록 가스의 유량을 조절하였다. 투과도는 가시광선(380 ~ 780 nm) 범위에서 측정하였고 두께와 표면조도는 AFM으로 측정하였다. 투과도는 $C_2H_2+Ar$의 Ar 가스 비율이 증가할수록 증가해 140 : 60일 때 최댓값을 나타낸 후 다시 감소하였다. $C_2H_2+N_2$ 투과도는 $N_2$ 가스 비율이 증가할수록 감소하는 경향을 나타내었다. 표면 거칠기는 $C_2H_2+Ar$ 혼합 가스를 사용한 경우의 Ar의 가스 비율이 증가할수록 증가하였다. 그러나 $C_2H_2+N_2$ 혼합 가스를 사용한 경우에는 $N_2$ 가스의 혼합 비율이 증가할수록 감소하였다.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.47 no.2
• /
• pp.15-20
• /
• 2010

In this study, AZO (Al: 3 wt%) thin films have been prepared on PES Plastic substrates at various working pressure (5~20 mTorr), $O_2$ gas flow rate(0~3%) and the fixed substrate temperature of 200 f by using the RF magnetron sputtering and their optical and electrical properties have been studied. The XRD measurement shows that AZO thin films exhibit c-axis preferred orientation. From the results of AFM measurements, it is known that the lowest surface roughness (3.49 nm) is obtained for the AZO thin film fabricated at 5 mTorr of working pressure and 3% of $O_2$ gas flow rate. The optical transmittance of AZO thin films is measured as 80% in the visible region. We observe that the energy band gap of AZO thin films increases with decreasing the working pressure and the $O_2$ gas flow rate. This phenomenon is due to the Burstein-Moss effect. Hall measurement shows that the maximum carrier concentration ($2.63\;{\times}\;10^{20}\;cm^{-3}$) and the minimum resistivity ($4.35\;{\times}\;10^{-3}\;{\Omega}cm$) are obtained for the AZO thin film fabricated at 5mTorr of working pressure and 0% of $O_2$ gas flow rate.

• Korean Journal of Optics and Photonics
• /
• v.13 no.3
• /
• pp.197-203
• /
• 2002

The TiO$_2$ coating solutions were synthesized with different concentrations (T1-0.7N, T2-2.0N) of hydrochloric acid used as catalyst. and TiO$_2$ thin films were prepared by sol-gel dip coating. Their structural and optical properties were examined as a function of calcination temperature. XRD results showed that T1 thin films calcined at 400~80$0^{\circ}C$ had the anatase phase, while those calcined at 100$0^{\circ}C$ had the rutile phase. T2 thin films calcined at 40$0^{\circ}C$ and $600^{\circ}C$ had the anatase phase, with the rutile phase for calcination at 80$0^{\circ}C$. Crystallinity of T2 thin films was superior to that of T1 thin films. The crystallite size of TiO$_2$ thin films increased with increasing calcination temperature, and the crystallite size of anatase phase in T2 thin films was larger than that in T1 thin films, but the crystallite size of rutile phase in T2 thin films was smaller. The surface morphology of the films showed that the films were formed more densely in the rutile phase than in the anatase phase, this phenomenon appeared conspicuously in T2 thin films. The transmittance of the samples with thin films on quartz glass calcined at 100$0^{\circ}C$ was significantly reduced at wavelength range about 300-700 nm due to the increased absorption originating from the change of crystallite phase and composition of the films and the scattering effect originating from increasing crystallite size. The refractive index of TiO$_2$ thin films increased, and hence the film thickness as well as the porosity of TiO$_2$ thin films decreased with increasing calcination temperature. Furthermore, the refractive index of T2 thin films was higher than T1 thin films, and porosity of T2 films was lower.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.44 no.5
• /
• pp.1-7
• /
• 2007

AZO thin films have been fabricated on quartz substrate with various Al doping concentrations and annealing temperatures by sol-gel method. The bset condition of (002) orientation and smooth surface (rms = 1.082 nm) is obtained for the AZO thin film doped with 1 mol % Al and annealed at 550 $^{\circ}C$. The optical transmittance of AZO thin films is higher than 80 % in the visible region. We observe that the energy band gap extends with increasing the Al doping concentration. This phenomenon is due to the Burstein-Moss effect. Through the measurement of Hall effect, it is observed that the AZO thin film has larger carrier concentration and smaller electrical resistivity than the pure ZnO thin film. However, the AZO thin film shows the decrease of carrier concentration and the increase of resistivity with the increase of Al concentration, that is due to the segregation of Al at grain boundaries. The maximum carrier concentration of $1.80{\times}10^{19}\;cm^{-3}$ and the minimum resistivity of 0.84 ${\Omega}cm$ are obtained for the AZO thin film doped with 1 mol % Al and annealed at 550 $^{\circ}C$.