• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.247.1-247.1
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• 2016

Low-cost, high efficiency solar cells are tremendous interests for the realization of a renewable and clean energy source. ZnTe based solar cells have a possibility of high efficiency with formation of an intermediated energy band structure by impurity doping. In this work, ZnO/ZnTe:Cr and ZnO/i-ZnTe structures were fabricated by pulsed laser deposition (PLD) technique. A pulsed (10 Hz) Nd:YAG laser operating at a wavelength of 266 nm was used to produce a plasma plume from an ablated a ZnTe target, whose density of laser energy was 10 J/cm2. The base pressure of the chamber was kept at approximately $4{\times}10-7Torr$. ZnTe:Cr and i-ZnTe thin films with thickness of 210 nm were grown on p-Si substrate, respectively, and then ZnO thin films with thickness of 150 nm were grown on ZnTe:Cr layer under oxygen partial pressure of 3 mTorr. Growth temperature of all the films was set to $250^{\circ}C$. For fabricating ZnO/i-ZnTe and ZnO/ZnTe:Cr solar cells, indium metal and Ti/Au grid patterns were deposited on back and front side of the solar cells by using thermal evaporator, respectively. From the fabricated ZnO/ZnTe:Cr and ZnO/i-ZnTe solar cell, dark currents were measured by using Keithley 2600. Solar cell parameters were obtained under Air Mass 1.5 Global solar simulator with an irradiation intensity of 100 mW/cm2, and then the photoelectric conversion efficiency values of ZnO/ZnTe:Cr and ZnO/i-ZnTe solar cells were measured at 1.5 % and 0.3 %, respectively.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.43.2-43.2
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• 2011

Single-walled carbon nanotubes (SWCNT) are transparent in the visible and show conductivity comparable to copper, and are environmentally stable. SWCNT films have high flexibility, conductivity and transparency approaching that indium tin oxide (ITO), and can be prepared inexpensively without vacuum equipment. Transparent conducting Films (TCF) of SWCNTs has the potential to replace conventional transparent conducting oxides (TCO, e.g. ITO) in a wide variety of optoelectronic devices, energy conversion and photovoltaic industry. However, the sheet resistance of SWCNT films is still higher than ITO films. A decreased in the resistivity of SWCNT-TCFs would be beneficial for such an application. We fabricated SWCNT sheet with $KAuBr_4$ on PET substrate. Arc-discharge SWCNTs were dispersed in deionized water by adding sodum dodecyl sulfate (SDS) as surfactant and sonicated, followed by the centrifugation. The dispersed SWCNT was spray-coated on PET substrate and dried on a hotplate at $100^{\circ}C$. When the spray process was terminated, the TCF was immersed into deionized water to remove the surfactant and then it was dried on hotplate. The TCF film was then treated with AuBr4-, rinsed with deionized water and dried. The surface morphology of TCF was characterized by field emission scanning electron microscopy. The sheet resistance and optical transmission properties of the TCF were measured with a four-point probe method and a UV-visible spectrometry, respectively. $HNO_3$ treated SWCNT films with Au nano-particles have the lowest 61 ${\Omega}$/< sheet resistance in the 80% transmittance. Sheet resistance was decreased due to the increase of the hole concentration at the washed SWCNT surface by p-type doping of $AuBr_4{^-}$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1096_1097
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• 2009

Aluminium doped zinc oxide(ZnO:Al) thin film, which is mainly used as a transparent conducting electrode in electronic devices, has many advantages compared with conventional indium tin oxide(ITO). In this paper in order to investigate the possible application of ZnO:Al thin films as a transparent conducting electrode for flexible film-typed dye sensitized solar cell (FT-DSCs), ZnO:Al and ITO thin films were prepared on the polyethylene terephthalate (PET) substrate by r. f. magnetron sputtering method. Specially one-inched FT-DSCs using either a ZnO:Al or ITO electrode were also fabricated separately under the same manufacturing conditions. Some properties of both the FT-DSCs with ZnO:Al and ITO transparent electrodes, such as conversion efficiency, fill factor, and photocurrent were measured and compared with each other. The results showed that by doping the ZnO target with 2 wt% of $Al_2O_3$, the film deposited at discharge power of 200W resulted in the minimum resistivity of $2.2\times10^{-3}\Omega/cm$ and at ransmittance of 91.7%, which are comparable with those of commercially available ITO. Two types of FT-DSCs showed nearly the same tendency of I-V characteristics and the same value of conversion efficiencies. Efficiency of FT-DSCs using ZnO:Al electrode was around 2.6% and that of fabricated FT-DSCs using ITO was 2.5%. This means that ZnO:Al thin film can be used in FT-DSCs as a transparent conducting layer.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.566-566
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• 2012

그래핀(Graphene)은 모든 탄소 동소체의 기본구성 요소로 2 차원 결정구조를 가지며, 양자홀 효과(quantum Hall effect), 뛰어난 열 전도도, 고 탄성, 광학적 투과성 등과 같은 탁월한 물리적 성질을 보이는 물질이다. 이러한 그래핀의 우수한 특성은 전계 효과 트랜지스터(field effect transistor), 화학/바이오 센서, 투명 전극(transparent electrode) 등의 다양한 전자소자를 개발하는 응용 가능하다. 그 중, 그래핀 투명전극의 제조는 가장 응용가능성이 높은 분야이다. 현재 투명전극 물질로는 인듐-주석 산화물(indium tin oxide; ITO)가 널리 이용되고 있으나, 인듐의 고갈로 인한 공급부족 문제 및 고 생산비용, 휘어지지 않는 취성 등의 단점을 지니고 있다. 따라서, 우수한 광학적 투과성과 전기전도성을 지닌 그래핀이 ITO의 대체 물질로서 각광받고 있다.[1-5] 본 연구에서는 그래핀의 투명전도필름의 응용을 위해 면저항을 낮추기 위한 방법으로 화학적 도핑(doping)을 이용하였다. 그래핀은 구리(copper; Cu) 호일을 촉매로 사용하여 열 화학증착법(Thermal Chemical Vapor Deposition)을 이용하여 합성하였다. 합성된 그래핀은 PMMA(Poly(methyl methacrylate)) 전사법을 이용하여 산화실리콘(SiO2) 기판에 전사 후, 염화은(AgCl)과 클로로벤젠(C6H5Cl)으로 만든 콜로이드(colloid) 용액에 디핑(dipping)하여 그래핀에 은 입자를 도핑 하였다. 그 결과, 은 입자 도핑 농도에 따라 면저항이 감소하는 양상을 보였다. 제작된 그래핀 투명전도성 필름의 투과도는 자외선-가시광선-근적외선 분광법(UV-Vis-NIR spectroscopy)를 이용하여 측정하였고, 라만 분광법(Raman spectroscopy)을 통해 그래핀 필름의 질적 우수성과 성장 균일도를 조사하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.237-238
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• 2008

본 연구에서는 APD 소자 제작시 주로 쓰이는 RTA에 의한 Zn 확산방법에 사용할 경우 undoped InP의 V/III비율에 따른 Zn원자의 확산, 도핑, 오믹저항의 성장을 조사하였다. RTA에 의한 확산 및 활성화 열처리 시 도핑 농도의 프로파일은 확산열처리만 한 경우보다 활성화 처리한 경우 더 커짐을 볼 수 있었다. SIMS 결과 활성화 처리 후 표면쪽에 Zn원자의 약간의 결핍현상을 보이는 데 이는 표면쪽에 Zn원자의 탈착이 약간 이루어지는 것으로 보인다. 이 원인은 결과적으로 오믹저항의 증가를 가져왔다.

• Transactions on Electrical and Electronic Materials
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• 제16권3호
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• pp.124-129
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• 2015

Organic electronics are the domain in which the components and circuits are made of organic materials. This new electronics help to realize electronic and optoelectronic devices on flexible substrates. In recent years, organic materials have replaced conventional semiconductors in many electronic components such as, organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic (OPVs). It is well known that organic light emitting diodes (OLEDs) have many advantages in comparison with inorganic light-emitting diodes LEDs. These advantages include the low price of manufacturing, large area of electroluminescent display, uniform emission and lower the requirement for power. The aim of this paper is to model polymer LEDs and OLEDs made with small molecules for studying the electrical and optical characteristics. The purpose of this modeling process is, to obtain information about the running of OLEDs, as well as, the injection and charge transport mechanisms. The first simulation structure used in this paper is a mono layer device; typically consisting of the poly (2-methoxy-5(2'-ethyl) hexoxy-phenylenevinylene) (MEH-PPV) polymer sandwiched between an anode with a high work function, usually an indium tin oxide (ITO) substrate, and a cathode with a relatively low work function, such as Al. Electrons will then be injected from the cathode and recombine with electron holes injected from the anode, emitting light. In the second structure, we replaced MEH-PPV by tris (8-hydroxyquinolinato) aluminum (Alq₃). This simulation uses, the Poole-Frenkel -like mobility model and the Langevin bimolecular recombination model as the transport and recombination mechanism. These models are enabled in ATLAS- SILVACO. To optimize OLED performance, we propose to change some parameters in this device, such as doping concentration, thickness and electrode materials.

• 한국산학기술학회논문지
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• 제10권7호
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• pp.1489-1496
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• 2009

비정질 인듐-갈륨-아연 산화물 박막트랜지스터를 모델링 하여서, 능동층의 구조, 두께, 평형상태의 전자밀도에 대응하는 박막트랜지스터의 특성을 연구하였다. 단일 능동층 박막트랜지스터의 경우, 능동층이 얇을 때 높은 전계효과이동도를 보였다. 문턱전압의 절대값은 능동층의 두께가 20 nm일 때 최저치를 보였으며, 문턱전압이하 기울기는 두께에 대한 의존성을 보이지 않았다. 복층구조 능동층의 경우, 하부의 능동층이 높은 평형상태 전자밀도를 가질 때보다 우수한 스위칭 특성을 보였다. 이 경우에도 능동층의 두께가 얇을 때에 높은 전계효과 이동도를 보였다. 높은 평형상태 전자밀도의 능동층의 두께를 증가시키면 문턱전압은 음의 방향으로 이동하였다. 문턱전압이하 기울기는 능동층의 구조에 대하여 특별한 의존성을 보이지 않았다. 이상과 같은 데이터는 산화물반도체 박막트랜지스터 능동층의 구조, 두께, 도핑비율을 최적화함에 효과적으로 사용될 것으로 기대된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.451-451
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• 2010

최근들어 80인치 이상의 대경 고화질 display 및 휴대용 projection display 제작이 가능한 LCoS (Liquid Crystal on Silicon) display에 대한 관심이 높아지고 있다. LCoS projection display는 높은 개구율, 빠른 응답속도, 고화질, 대형 디스플레이 임에도 불구하고 낮은 제조단가 등의 여러 가지 장점을 가지고 있다. LCoS projection display의 핵심 기술로는 높은 투과도와 낮은 반사율을 갖는 유리기판, 무기 배향막 증착 기술, Si back plane과의 접합기술 등이 있다. 이 중 LCoS projection display 제작을 위한 첫 단계인 유리기판은 가시광선 영역에서 96% 이상의 높은 투과도와 3% 미만의 반사도를 요구하는 기술을 필요로 한다. 본 연구에서는 indium이 doping된 tin oxide (ITO)를 투명 전도성막으로 사용하고, $SiO_2/MgF_2$ 이중 박막을 반사방지막으로 채택하여 고투과도 및 저반사율을 갖는 유리기판 제조에 응용하였다. 먼저 15nm 두께의 ITO 박막을 DC sputtering을 이용하여 8-inch 크기의 corning1737 유리기판 상에 증착한 후, 그 반대편에 e-beam evaporation 장비를 사용하여 120nm 두께의 반사 방지막을 증착하였다. 또한 유리기판 상에 증착된 투명 전도성막의 표면개질을 위하여 Ar plasma를 이용하여 treatment를 수행하였다. 이 때 sputtering 조건은 DC power, Ar 유량 및 압력을 조절함으로서 높은 투과도를 갖는 최적의 조건을 구현하였고, e-beam evaporation을 이용한 반사방지막 증착 조건은 $SiO_2$와 $MgF_2$의 계면에서 빛의 반사를 최소화할 수 있는 최적의 조건을 구현하였다. 제작된 유리기판은 가시광선 영역에서 97% 이상의 투과도를 보였으며, 최대 2.8%의 반사율을 보여, LCoS display 제작에 적합함을 확인할 수 있었다. 또한 Ar plasma 처리 후 ITO 박막의 면저항 값은 $100\;{\omega}/{\Box}$, 표면 거칠기는 rms 값 기준 0.095nm, 접촉각 $20.8^{\circ}$의 특성을 보여, 타 index matched transparent conducting oxide가 coating된 유리기판에 비해 우수한 특성을 보였다.

• 한국재료학회지
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• 제21권12호
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• pp.639-643
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• 2011

Zinc oxide as an optoelectronic device material was studied to utilize its wide band gap of 3.37 eV and high exciton biding energy of 60 meV. Using anti-site nitrogen to generate p-type zinc oxide has shown a deep acceptor level and low solubility. To increase the nitrogen solubility in zinc oxide, group 13 elements (aluminum, gallium, and indium) was co-added to nitrogen. The effect of aluminum on nitrogen solubility in a $3{\times}3{\times}2$ zinc oxide super cell containing 72 atoms was investigated using density functional theory with hybrid functionals of Heyd, Scuseria, and Ernzerhof (HSE). Aluminum and nitrogen were substituted for zinc and oxygen sites in the super cell, respectively. The band gap of the undoped super cell was calculated to be 3.36 eV from the density of states, and was in good agreement with the experimentally obtained value. Formation energies of a nitrogen molecule and nitric oxide in the zinc oxide super cell in zinc-rich conditions were lower than those in oxygen-rich conditions. When the number of nitrogen molecules near the aluminum increased from one to four in the super cell, their formation energies decreased to approach the valence band maximum to some degree. However, the acceptor level of nitrogen in zinc oxide with the co-incorporation of aluminum was still deep.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.42.2-42.2
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• 2010

Transparent conducting oxides (TCOs) are of significant importance for their applications in various devices, such as light-emitting diodes, thin-film solar cells, organic light-emitting diodes, liquid crystal displays, and so on. In order for TCOs to contribute to the performance improvement of these devices, TCOs should have high transmittance and good electrical properties simultaneously. Sn-doped $In_2O_3$ (ITO) is the most commonly used TCO. However, indium is toxic and scarce in nature. Thus, ZnO has attracted a lot of attention because of the possibility for replacing ITO. In particular, group III impurity-doped ZnO showed the optoelectronic properties comparable to those of ITO electrodes. Al-doped ZnO exhibited the best performance among various doped ZnO films because of the high substitutional doping efficiency. However, in order for the Al-doped ZnO to replace ITO in electronic devices, their electrical and optical properties should further significantly be improved. In this connection, different ways such as a variation of deposition conditions, different deposition techniques, and post-deposition annealing processes have been investigated so far. Among the deposition methods, RF magnetron sputtering has been extensively used because of the easiness in controlling deposition parameters and its fast deposition rate. In addition, when combined with post-deposition annealing in a reducing ambient, the optoelectronic properties of Al-doped ZnO films were found to be further improved. In this presentation, we deposited Al-doped ZnO (ZnO:$Al_2O_3$ = 98:2 wt%) thin films on the glass and sapphire substrates using RF magnetron sputtering as a function of substrate temperature. In addition, the ZnO samples were annealed in different conditions, e.g., rapid thermal annealing (RTA) at $900^{\circ}C$ in $N_2$ ambient for 1 min, tube-furnace annealing at $500^{\circ}C$ in $N_2:H_2$=9:1 gas flow for 1 hour, or RTA combined with tube-furnace annealing. It is found that the mobilities and carrier concentrations of the samples are dependent on growth temperature followed by one of three subsequent post-deposition annealing conditions.