• Current Photovoltaic Research
• /
• v.5 no.1
• /
• pp.15-19
• /
• 2017

The fossil fuel power consumption generates $CO_2$, which causes the problems such as global warming. Also, the increase in energy consumption has accelerated the depletion of the fossil fuels, and renewable energy is attracting attention. Among the renewable energies, the solar energy gets a lot of attention as the infinite clean energy source. But, the supply level of solar cell is insignificant due to high cost of generation of electric power in comparison with fossil fuels. Thus several researchers are recently doing the research on ultra-low-cost solar cells. Also, $Cu_2O$ is one of the applied materials as an absorption layer in ultra-low-cost solar cells. Cuprous oxide ($Cu_2O$) is highly desirable semiconductor oxide for use in solar energy conversion due to its direct band gap ($E_g={\sim}2.1eV$) and a high absorption coefficient that absorbs visible light of wavelengths up to 650 nm. In addition, $Cu_2O$ has several advantages such as non-toxicity, low cost and can be prepared with simple and cheap methods on large scale. In this work, we fabricated the $Cu_2O$ thin films by reactive sputtering method. The films were deposited with a Cu target with variable parameters such as substrate temperature, rf-power, and annealing condition. Finally, we confirmed the structural properties of thin films by XRD and SEM.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.10
• /
• pp.625-630
• /
• 2017

ZnS was chemically deposited as a buffer layer alternative to CdS, for use as a Cd-free buffer layer in $Cu(In_{1-x}Ga_x)Se_2$ (CIGS) solar cells. The deposition of a thin film of ZnS was carried out by chemical bath deposition, following which the structural and optical properties of the ZnS layer were studied. For the experiments, zinc sulfate hepta-hydrate ($ZnSO_4{\cdot}7H_2O$), thiourea ($SC(NH_2)_2$), and ammonia ($NH_4OH$) were used as the reacting agents. The mole concentrations of $ZnSO_4$ and $SC(NH_2)_2$ were fixed at 0.03 M and 0.8 M, respectively, while that of ammonia, which acts as a complexing agent, was varied from 0.3 M to 3.5 M. By varying the mole concentration of ammonia, optimal values for parameters like optical transmission, deposition rate, and surface morphology were determined. For the fixed mole concentrations of $0.03M\;ZnSO_4{\cdot}7H_2O$ and $0.8M\;SC(NH_2)_2$, it was established that 3.0 M of ammonia could provide optimal values of the deposition rate (5.5 nm/min), average optical transmittance (81%), and energy band gap (3.81 eV), rendering the chemically deposited ZnS suitable for use as a Cd-free buffer layer in CIGS solar cells.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.9
• /
• pp.837-840
• /
• 2015

Graphene is a single layer of carbon material which shows very high electron mobility, so many kinds of research on the devices using graphene layer have been performed so far. Graphene material is adequate for high frequency and fast operation devices due to its higher mobility. In this research, the actual graphene layer is evaluated using RT-CVD method which can be available for mass production. The mobility of $7,800cm^2/Vs$ was extracted, that is more than 7 times of that in silicon substrate. The graphene transistor model having no band gap is evaluated using both of pMOS and nMOS based on the measured mobility values. And then the response of graphene transistor model regarding to gate length and width is examined.

• Journal of the Korean Magnetics Society
• /
• v.15 no.4
• /
• pp.231-235
• /
• 2005

We studied the microstructural evolution of ZrTM-Al (TM=Nb and Ti) alloy films, MR and electrical properties of the MTJ with $ZrTM-AlO_x$ barrier as a function of Zr/TM ratio. We observed that the ternary-oxide barrier reduced the TMR ratio due mainly to the structural defects such as the surface roughness. The change in TMR ratio and $V_h$ with Zr/TM ratio exactly corresponds to the systematic changes in the microstructural variation. Although the MTJ with ternary oxide reduced the TMR and the electrical stabilities, the junction resistances decreased as the Ti and Nb concentration increased due to the band-gap reduction caused by the formation of extra bands

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.36D no.12
• /
• pp.11-20
• /
• 1999

We have designed and fabricated direct-and gap-coupled microstrip hairpin-comb filters by patterning double-sided YBCO films on a single 50-mm-diameter, 0.5-mm-thick $LaAlO_3$ wafer. Both filters have a center frequency at 1.773 GHz, 12 MHz bandwidth, 0.5 dB minimum insertion loss in the passband, and very strong out-of- band rejection. Due to two attenuation poles below and above the passband, the direct-coupled hairpin-comb filter showed a better skirt characteristic than the gapcoupled hairpin-comb filter which had only one attenuation pole below the passband.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.16 no.3
• /
• pp.558-564
• /
• 2012

We fabricated Ga doped ZnO (GZO) thin films on the glass substrate (Eagle 2000) with various of Ga doping concentration and annealing temperatures using sol-gel method, electrical and optical properties were investigated. When the GZO thin films doped with 1 mol% of Ga and annealed at $600^{\circ}C$, the excellent (002) orientation was observed. In the results of Hall measurement, carrier concentration decreased and resistivity increased due to segregation effect with increasing of the Ga doping concentration. The largest carrier concentration and lowest resistivity were $9.13{\times}10^{18}cm^{-3}$ and $0.87{\Omega}cm$, respectively, in the GZO thin films doped with 1 mol% Ga and annealed at $600^{\circ}C$. All films is higher than 80 % in the visible light region. Energy band gap narrowing due to Burstein-Moss effect was observed with increasing of Ga doping concentration from 1 to 4 mol%.

• Applied Chemistry for Engineering
• /
• v.28 no.5
• /
• pp.571-575
• /
• 2017

In this study, cadmium telluride (CdTe) quantum dots were synthesized by using ultrasonic irradiation method. Optical properties and structural characteristics of the CdTe quantum dots were analyzed by two main variables; the ratio of the precursor and the synthesis time. As the synthesis time increased, the band gap reduction was observed with the growth of CdTe quantum dots. As for the luminescence properties, the red shift appeared at 510~610 nm wavelength range. Also, it was confirmed that the red shift occurs rapidly as the ratio of Te increases. According to PL peak intensity, the highest intensity was shown at 180 to 240 min. Structural characteristics of CdTe quantum dots were investigated through XRD and TEM, and the cubic zinc blend structure was observed. The size of quantum dots was about 2.5 nm and uniformly dispersed when the synthesis time took 210 min. In addition, the apparent crystallinity was discovered in FFT image.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2014.11a
• /
• pp.27-28
• /
• 2014

투명전극이란 전기 전도도를 갖는 동시에 가시광선 영역에서 빛을 투과하는 성질을 가지는 소재이다. 일반적으로 가시광선 영역(380nm~780nm)에서 80%이상의 광 투과도를 가지며, 비저항이 $10^{-3}{\Omega}{\cdot}cm$ 이하, optical band gap 이 3.3 eV 이상인 물질을 TCO(Transparent Conducting oxide)라고 한다. 현재까지 국내의 TCO 관련 연구는 터치패널, 디스플레이, 태양전지 등 광전자분야에서 가장 널리 사용되고 있는 ITO(Sn:In2O3)에 치중되어 있으며, 관련 연구도 거의 디스플레이 맞춤형 연구개발이 주류를 이루어왔다. ITO가 전기전도성이 우수하고 동시에 가시광선 영역에서의 투과율도 80%이상으로 전기적, 광학적 특성이 우수하다는 장점을 가지고 있으나, In의 희소성으로 인한 고가격, 유독성, 접착력 문제 때문에 이를 대체하기 위해 제조원가가 ITO에 비하여 월등히 저렴하고 내화학성과 내마모성이 우수하면서도, 가시광선 영역에서의 광투과율이 80%이상으로 좋다는 $SnO_2$에 관한 연구가 활발히 진행되어 왔다. 적절한 dopant를 첨가하여 $SnO_2$자체의 높은 광학적 투과도를 유지하면서 전기전도성을 더 높일수 있고, 투명전극이 가져야 할 고온 안정성을 가지고 있으며 비독성이고 수소 플라즈마에 대한 내성이 더 클 뿐만 아니라 저온에서 성장이 가능하다. $SnO_2$의 전기 전도도를 높이기 위한 Al, In, Ga, B와 같은 3족 원소가 $SnO_2$의 n형 dopant로 널리 사용되고 있다. 그 중 Al은 반응성이 커서 박막 증착 중에 산화되기 쉬운 반면, 전기적 특성 및 광학적 특성의 향상을 이룰 수 있다. 본 연구에서는 Rf Sputtering법을 사용하여 quartz기판 위에 다층박막 형태의 투명전도막을 제작한 후, 열처리를 수행, 이에 의한 다층박막 내 계면간 상호확산 현상을 이용하여 투명 전도막의 특성변화를 관찰하였다. 박막의 구조적 특성은 XRD장비를 사용하여 분석하였으며, 전기적, 광학적 특성은 각각 표면저항기, 홀 측정 장비, 그리고 UV-VIS-NI를 사용하여 확인하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2014.11a
• /
• pp.264-265
• /
• 2014

This Paper reports the photocatalytic activity of $g-C_3N_4/NaTaO_3$ hybrid composite photocatalysts synthesized by ball-mill method. The $g-C_3N_4$ and $NaTaO_3$ were individually prepared by Solid state reaction and microwave hydrothermal process, respectively. The $g-C_3N_4/NaTaO_3$ composite showed the enhanced photocatalytic activity for degradation of rhodamine B dye (Rh. B) under simulated solar light irradiation. The results revealed that the band-gap energy absorption edge of hybrid composite samples was shifted to a longer wavelength as compared to $NaTaO_3$ and the 50 wt% $g-C_3N_4/NaTaO_3$ hybrid composite exhibited the highest percentage (99.6 %) of degradation of Rh. B and the highest reaction rate constant ($0.013min^{-1}$) in 4 h which could be attributed to the enhanced absorption of the hybrid composite photocatalyst in the UV-Vis region. Hence, these results suggest that the $g-C_3N_4/NaTaO_3$ hybrid composite exhibits enhanced photocatalytic activity for the degradation of rhodamine B under simulated solar light irradiation in comparison to the commercial $NaTaO_3$.

• Journal of the Korean Ceramic Society
• /
• v.41 no.1
• /
• pp.57-61
• /
• 2004

Zinc Oxide (ZnO) have the crystal structure of wurtzite which is semiconducting oxide with band gap energy of 3.3eV. $In_2O_3$-doped ZnO films were fabricated by electron beam evaporation at $400^{\circ}C$ and their characteristics were investigated. The content of $In_2O_3$ in ZnO films had a marked effect on the electrical properties of the films. As $In_2O_3$ content decreased. $In_2O_3$-doped ZnO films was converted amorphous into crystallized films and showed a better characteristics generally as a transparent conducting oxide. As $In_2O_3$-doped ZnO films were prepared by $In_2O_3$-doped ZnO pellet with 0.2at% of $In_2O_3$ content, the value of resistivity was about $6.0 {\times} 10^{-3} {\Omega}cm$. The transmittance was higher than 85% throughout the visible range.