• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.315-315
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• 2016

The hydrogenated amorphous silicon (a-Si:H) thin film solar cells using n/Al or n/Ag/Al back reflector have low short circuit current (Jsc) due to high absorption coefficients of Al or work function difference between n-layer and the metal. In this article, we utilized aluminum doped zinc oxide (AZO) to raise the internal reflectance for the improvement of short current density (Jsc) in a-Si:H thin film solar cells. It was found that there was a slight increase in the reflectance in the long wavelength range at the process temperature of 125oC due to improved crystalline quality of the AZO back reflector. The optical band gap (Eg) and work function were affected by the temperature and so did the internal reflectance. The increased internal reflectance within the solar cell resulted in Jsc of 14.94 mA/cm2 and the efficiency of 8.84%. Jsc for the cell without back reflector was 12.29 mA/cm2.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.452-452
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• 2013

ZnO is one of the most attractive transparent conductive oxide (TCO) films because of low toxicity, a wide band gap material and relatively low cost. However, the electrical conductivity of un-doped ZnO is too high to use it as TCO films in practical application. To improve electrical properties of undoped ZnO, transition metal (TM) doped ZnO films such as Al doped ZnO or Ti doped ZnO have been extensively studied. Here, we prepared Ti doped ZnO thin films by atomic layer deposition (ALD) for the application of TCO films. ALD was used to prepare Ti-doped ZnO thin films due to its inherent merits such as large area uniformity, precise composition control in multicomponent thin films, and digital thickness controllability. Also, we demonstrated that ALD method can be utilized for fabricating highly ordered freestanding nanostructures of Ti-doped ZnO thin films by combining with BCP templates, which can potentially used in the photovoltaic applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.340.1-340.1
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• 2014

본 실험에서는 Ag두께 변화에 따른 투과율과 Energy bandgap의 변화를 알아보기 위해 RF Sputter장비와 Evaporator장비를 사용하여 IGZO, ZnO, AZO OMO 구조로 Low-e 코팅된 Glass를 제작하였다. $3cm{\times}3cm$의 Corning1737 유리기판에 RF Sputtering 방식으로 Oxide layer를 증착 하였고 Evaporator장비로는 Metal layer인 Ag막을 증착하였다. Oxide layer 증착 시 RF Sputter장비의 조건은 $3.0{\times}10^{-6}Torr$이하로 하였으며, 증착압력은 $6.0{\times}10^{-3}Torr$, 증착온도는 실온으로 고정하였다. Metal layer 증착 시 Evaporator장비의 조건은 $5.0{\times}10^{-6}Torr$이하, 전압은 0.3 V, Rotate 2 rpm으로 고정하였다. 실험 변수로는 Ag 두께를 5,7,9,11,13 nm로 변화를 주어 실험을 진행하였다. 투과도 측정 장비를 사용하여 각 샘플을 측정한 결과 IGZO의 경우 가시광영역의 평균 투과율이 80% 이상이며 Ag두께가 5nm일 때부터 자외선 영역의 빛을 차단하여 low-e 특성을 나타내었다. 이는 산화물인 IGZO가 결정질인 AZO, ZnO 보다 낮은 표면거칠기를 가지기 때문이다. Ag 두께에 따른 각 물질의 Optical energy bandgap 분석결과 Ag 두께가 증가할수록 IGZO는 4.65~4.5 eV, AZO는 4.6~4.4 eV, ZnO는 4.55~4.45 eV로 Energy bandgap은 감소하였다. AFM장비를 이용하여 각 샘플의 표면 Roughness 측정 결과 Ag 두께가 증가할수록 표면거칠기도 증가하는 경향을 나타내었다.

• 한국전기전자재료학회논문지
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• 제30권8호
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• pp.508-513
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• 2017

Ultraviolet (UV) photodetectors are used in various industries and fields of research, including optical communication, flame sensing, missile plume detection, astronomical studies, biological sensors, and environmental research. However, general UV detectors that employ Schottky junction diodes and p-n junctions have high fabrication cost and low quantum efficiency. In this study, we investigated the characteristics of materials used to manufacture UV photodetectors in a low-cost solution process that requires easy fabrication of flexible substrates. We fabricated p-type NiO and n-type ZnO substrates with wide band gap by the sol-gel method and compared the characteristics of substrates prepared under different spin-coating and heat-treatment conditions.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.108-109
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• 2006

ZnO semiconductor has a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV, and displays excellent sensing and optical properties. In particular, ZnO based 1D nanowires and nanorods have received intensive attention because of their potential applications in various fields. We grew ZnO buffer layers prior to the growth of ZnO nanorods for the fabrication of the vertically well-aligned ZnO nanorods without any catalysts. The ZnO nanorods were grown on Si (111) substrates by vertical MOCVD. The ZnO buffer layers were grown with various thicknesses at $400^{\circ}C$ and their effect on the formation of ZnO nanorods at $300^{\circ}C$ was evaluated by FESEM, XRD, and PL. The synthesized ZnO nanorods on the ZnO film show a high quality, a large-scale uniformity, and a vertical alignment along the [0001]ZnO compared to those on the Si substrates showing the randomly inclined ZnO nanorods. For sample using ZnO buffer layer, 1D ZnO nanorods with diameters of 150-200 nm were successively fabricated at very low growth temperature, while for sample without ZnO buffer the ZnO films with rough surface were grown.

• 대한금속재료학회지
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• 제48권12호
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• pp.1109-1115
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• 2010

ZnO thin films were deposited on Si(100) substrates at low temperatures ($44^{\circ}C{\sim}210^{\circ}C$) by atomic layer deposition using DEZn (diethyl zinc) and water as precursors. The film thickness was measured by ellipsometry calibrated with cross-sectional TEM. The phase formation, microstructure evolution, UV-absorbance, and chemical composition changes were examined by XRD, SEM, AFM, TEM, UV-VIS-NIR, and AES, respectively. A uniform amorphous ZnO layer was formed even at $44^{\circ}C$ while stable crystallized ZnO films were deposited above $90^{\circ}C$. All the samples showed uniform surface roughness below 3 nm. Fully crystallized ZnO layers with a band-gap of 3.37 eV without carbon impurities can be formed at substrate temperatures of less than $90^{\circ}C$.

• 한국재료학회지
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• 제29권8호
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• pp.477-482
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• 2019

The magnetic properties and electronic structures of the B20 crystal structure MnGe and MnSi were investigated using the density functional theory with local density approximation. The low symmetry of the B20 crystal structure plays a very important role to make electromagnetic characteristics of these materials. The important result of the calculations is that it can be observed the appearance of a pair of gaps in the density of states near the Fermi level in both compounds. These features are results from d-band splitting by the low symmetry of the crystal field from B20 crystal structure. It can be seen that there is half-metallic characteristics from the density of states in both compounds. The calculation shows that the value of magnetic moment of MnGe is 5 times bigger than that of MnSi even though they have same crystal structure. The electronic structures of paramagnetic case have a very narrow indirect gap just above the Fermi level in both compounds. These gaps acquire some significance in establishing the stability of the ferromagnetic states within the local density approximation. Calculation shows that the Mn 3d character dominates the density of states near the Fermi level in both materials.

• 한국재료학회지
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• 제32권6호
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• pp.287-292
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• 2022

Magnesium-antimonide is a well-known zintl phase thermoelectric material with low band gap energy, earth-abundance and characteristic electron-crystal phonon-glass properties. The nominal composition Mg_3.8-xZn_xSb₂ (0.00 ≤ x ≤ 0.02) was synthesized by controlled melting and subsequent vacuum hot pressing method. To investigate phase development and surface morphology during the process, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out. It should be noted that an additional 16 at. % Mg must be added to the system to compensate for Mg loss during the melting process. This study evaluated the thermoelectric properties of the material in terms of Seebeck coefficient, electrical conductivity and thermal conductivity from the low to high temperature regime. The results demonstrated that substituting Zn at Mg sites increased electrical conductivity without significantly affecting the Seebeck coefficient. The maximal dimensionless figure of merit achieved was 0.30 for x = 0.01 at 855 K which is 30% greater than the intrinsic value. Electronic flow properties were also evaluated and discussed to explain the carrier transport mechanism involved in the thermoelectric properties of this alloy system.

• 한국진공학회지
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• 제21권3호
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• pp.136-141
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• 2012

열처리 공정으로 제조한 $In_2Se_3$ 박막의 구조 및 광학적 물성을 조사하여 보고한다. 기판위에 스퍼터링 방법으로 인듐(In: indium)을 증착하고 셀레늄 분위기에서 열처리 온도를 변화시키며 In-Se 박막을 제조하였다. 열처리 온도가 증가함에 따라 $In_2Se_3$ 박막의 형성과 상의 변화를 관찰 할 수 있었다. 낮은 열처리 온도(${\leq}150^{\circ}C$)에서는 In의 뭉침 현상을 관찰할 수 있었고 열처리 온도가 $250^{\circ}C$ 부터 $In_2Se_3$ 박막이 형성되며 $350^{\circ}C$ 에서 ${\gamma}-In_2Se_3$ 상이 형성됨을 알 수 있었다. 열처리 온도가 $400^{\circ}C$로 증가면 wurtzite 구조의 고품질 ${\gamma}-In_2Se_3$ 박막을 얻을 수 있었다. 열처리 온도가 증가함에 따라 $In_2Se_3$ 박막의 밴드갭이 증가함을 알 수 있었고, 열처리 온도 $400^{\circ}C$에서 제조된 ${\gamma}-In_2Se_3$ 결정질 박막의 밴드갭이 1.796eV임을 알았다.

• 전기전자학회논문지
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• 제12권3호
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• pp.176-183
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• 2008

본 논문에서는 DTMOS(Dynamic Threshold voltage MOSFET) 스위칭 소자를 사용한 고 효율 전원 제어 장치 (PMIC)를 제안하였다. 높은 출력 전류에서 고 전력 효율을 얻기 위하여 PWM(Pulse Width Modulation) 제어 방식을 사용하여 PMIC를 구현하였으며, 낮은 온 저항을 갖는 DTMOS를 설계하여 도통 손실을 감소시켰다. 벅 컨버터(Buck converter) 제어 회로는 PWM 제어회로로 되어 있으며, 삼각파 발생기(Saw-tooth generator), 밴드갭기준 전압 회로(Band-gap reference circuit), 오차 증폭기(Error amplifier), 비교기(Comparator circuit)가 하나의 블록으로 구성되어 있다. 삼각파 발생기는 그라운드부터 전원 전압(Vdd:3.3V)까지 출력 진폭 범위를 갖는 1.2MHz 발진 주파수를 가지며, 비교기는 2단 연산 증폭기로 설계되었다. 그리고 오차 증폭기는 70dB의 DC gain과 $64^{\circ}$ 위상 여유를 갖도록 설계하였다. Voltage-mode PWM 제어 회로와 낮은 온 저항을 스위칭 소자로 사용하여 구현한 DC-DC converter는 100mA 출력 전류에서 95%의 효율을 구현하였으며, 1mA이하의 대기모드에서도 높은 효율을 구현하기 위하여 LDO를 설계하였다.