• Current Photovoltaic Research
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• 제1권2호
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• pp.115-121
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• 2013

ZnO film has been used for CIGS solar cells as a buffer layer as itself or by doping Mg and Sn; ZnO film also has been used as a transparent conducting layer by doping Al or B for solar cells. Since ZnO itself is a host material for many applications it is necessary to understand the electrical and optical properties of ZnO film itself with various preparation conditions. We prepared ZnO films by converting ZnS precursor into ZnO film by thermal annealing. ZnO film was formed at low temperature as low as $500^{\circ}C$ by annealing a ZnS precursor layer in air. In the air annealing, the electrical resistivity decreased monotonically with increasing annealing temperature; the intensity of the green photoluminescence at 505 nm increased up to $750^{\circ}C$ annealing. The electrical resistivity further decreased and the intensity of green emission also increased in reducing atmospheres. The results suggest that deep-level defects originated by oxygen vacancy enhanced green emission, which reduce light transmittance and enhance the recombination of electrons in conduction band and holes in valence. More oxidizing environment is necessary to obtain defect-free ZnO film for higher transparency.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.238-239
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• 2010

Dimethyl sulphoxide (DMSO) is one of the widely-used secondary dopants in order to enhance the conductivity of poly(3, 4-ethylenedioxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS) film. In this work, we investigated the effect of DMSO doping in to PEDOT:PSS on the electrical performance of the bulk heterojunction photovoltaics consisting of poly(3-hexylthiophene-2, 5-diyl) and phenyl-C61-butyric acid methyl ester. Correlation between the power conversion efficiency and the mechanism of improving conductivity, surface morphology, and contact properties was examined. The PEDOT:PSS films, which contain different concentration of DMSO, have been prepared and annealed at different annealing temperatures. The mixture of DMSO and PEDOT:PSS was prepared with a ratio of 1%, 5%, 15%, 25%, 35%, 45%, 55% by volume of DMSO, respectively. The DMSO-contained PEDOT:PSS solutions were stirred for 1hr at $40^{\circ}C$, then spin-coated on the ultra-sonicated glass. The spin-coated films were baked for 10min at $65^{\circ}C$, $85^{\circ}C$, and $120^{\circ}C$ in air. In order to investigate the electrical performance, P3HT:PCBM blended film was deposited with thickness of 150nm on DMSO-doped PEDOT:PSS layer. After depositing 100nm of Al, the device was post-annealed for 30min at $120^{\circ}C$ in vacuum. The fabricated cells, in this study, have been characterized by using several techniques such as UV-Visible spectrum, 4-point probe, J-V characteristics, and atomic force microscopy (AFM). The power conversion efficiency (AM 1.5G conditions) was increased from 0.91% to 2.35% by tuning DMSO doping ratio and annealing temperature. It is believed that the improved power conversion efficiency of the photovoltaics is attributed to the increased conductivity, leading to increasing short-circuit current in DMSO-doped PEDOT:PSS layer.

• 한국재료학회지
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• 제18권4호
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• pp.199-203
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• 2008

High-efficiency phosphorescent organic light emitting diodes using TCTA-TAZ as a double host and $Ir(ppy)_3$ as a dopant were fabricated and their electro-luminescence properties were evaluated. The fabricated devices have the multi-layered organic structure of 2-TNATA/NPB/(TCTA-TAZ) : $Ir(ppy)_3$/BCP/SFC137 between an anode of ITO and a cathode of LiF/AL. In the device structure, 2-TNATA[4,4',4"-tris(2-naphthylphenyl-phenylamino)-triphenylamine] and NPB[N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine] were used as a hole injection layer and a hole transport layer, respectively. BCP [2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline] was introduced as a hole blocking layer and an electron transport layer, respectively. TCTA [4,4',4"-tris(N-carbazolyl)-triphenylamine] and TAZ [3-phenyl-4-(1-naphthyl)-5-phenyl-1,2,4-triazole] were sequentially deposited, forming a double host doped with $Ir(ppy)_3$ in the [TCTA-TAZ] : $Ir(ppy)_3$ region. Among devices with different thickness combinations of TCTA ($50\;{\AA}-200\;{\AA}$) and TAZ ($100\;{\AA}-250\;{\AA}$) within the confines of the total host thickness of $300\;{\AA}$ and an $Ir(ppy)_3$-doping concentration of 7%, the best electroluminescence characteristics were obtained in a device with $100\;{\AA}$-think TCTA and $200\;{\AA}$-thick TAZ. The $Ir(ppy)_3$ concentration in the doping range of 4%-10% in devices with an emissive layer of [TCTA ($100\;{\AA}$)-TAZ ($200\;{\AA}$)] : $Ir(ppy)_3$ gave rise to little difference in the luminance and current efficiency.

• 한국전기전자재료학회논문지
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• 제28권10호
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• pp.665-669
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• 2015

We investigated and compared two methods of in-situ oxidation and chemical etching treatment (CET) to remove the boron rich layer (BRL). The BRL is generally formed during boron doping process. It has to be controlled in order not to degrade carrier lifetime and reduce electrical properties. A boron emitter is formed using $BBr_3$ liquid source at $930^{\circ}C$. After that, in-situ oxidation was followed by injecting oxygen of 1,000 sccm into the furnace during ramp down step and compared with CET using a mixture of acid solution for a short time. Then, we analyzed passivation effect by depositing $Al_2O_3$. The results gave a carrier lifetime of $110.9{\mu}s$, an open-circuit voltage ($V_{oc}$) of 635 mV at in-situ oxidation and a carrier lifetime of $188.5{\mu}s$, an $V_{oc}$ of 650 mV at CET. As a result, CET shows better properties than in-situ oxidation because of removing BRL uniformly.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.159-159
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• 2010

본 논문은 테라헤르츠 소스로 저온 InGaAs를 대체하기 위한 저온 $In_{0.64}Al_{0.36}Sb$의 실리콘(Si) 도핑 농도에 따른 광학적 특성 변화를 photoluminescence (PL)과 time-resolved PL (TRPL) 측정을 이용하여 분석하였다. $In_{0.64}Al_{0.36}Sb$ 시료는 분자선 엑피탁시 (molecular beam epitaxy)법으로 GaAs 기판 위에 약 $420^{\circ}C$에서 $3.7\;{\mu}m$ 두께 성장하였다. Si은 $In_{0.64}Al_{0.36}Sb$ 시료에서 도핑 농도가 낮을 때는 어셉터(acceptor)로 작용하다가 도핑 농도가 증가함에 따라 도너(donor)로 작용하였다. 본 연구에 사용한 $In_{0.64}Al_{0.36}Sb$ 시료의 Si 도핑 농도는 $4.5{\times}10^{16}\;cm^{-3}$ (n형), $4{\times}10^{16}\;cm^{-3}$ (n형), $8{\times}10^{15}\;cm^{-3}$ (n형), $1{\times}10^{15}\;cm^{-3}$ (p형), $4{\times}10^{14}\;cm^{-3}$ (p형)인 다섯 개의 시료를 사용하였다. Si 도핑한 시료의 PL 피크는 undoped 시료보다 약 100-200 nm 단파장에서 나타나고 PL 세기도 크게 증가하였다. 그러나 Si 도핑 농도가 가장 낮은 n형과 p형 시료의 PL 피크가 가장 짧은 파장 (높은 에너지)에 나타나고 도핑 농도가 증가함에 따라 장파장으로 이동함을 보였다. n형 시료의 도핑 농도가 $8{\times}10^{15}\;cm^{-3}$에서 $4.5{\times}10^{16}\;cm^{-3}$로 증가하였을 때 PL 피크는 1232 nm에서 1288 nm까지 장파장쪽으로 이동하였으며, p형 시료는 도핑 농도가 $4{\times}10^{14}\;cm^{-3}$에서 $1{\times}10^{15}\;cm^{-3}$로 증가하였을 때 PL 피크가 1248 nm에서 1314 nm로 이동함을 보였다. 또한 시료 온도에 따른 PL 결과는 온도가 증가함에 따라 PL 피크는 장파장으로 이동하면서 PL 세기는 급격하게 감소하고 약 100 - 150 K에서 소멸하였다. 그러나 ~1500 nm 이상 장파장 영역에 매우 넓은 새로운 피크가 나타났으며 온도가 증가함에 따라 PL 세기가 증가함을 확인하였다. Si 도핑 농도에 따른 운반자 수명시간 변화를 TRPL을 이용하여 측정하였다. 운반자 수명시간은 double exponential function을 이용하여 얻었다. Si 도핑 시료의 운반자 수명시간이 undoped 시료에 비해 매우 길게 나타났으며, Si 도핑 시료에서는 p형 시료들보다 n형 시료들의 운반자 수명시간이 길게 나타났다. PL 방출파장에 따른 운반자 수명시간은 Si 도핑 농도에 따라 다르게 나타났다. 이러한 PL과 TRPL 결과로부터 $In_{0.64}Al_{0.36}Sb$의 발광 특성 및 운반자 동역학은 Si 도핑에 크게 영향을 받는다는 것을 확인하였다.

• 전자공학회논문지D
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• 제36D권6호
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• pp.28-34
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• 1999

본 논문에서는 GaN 박막 위에 각각 알루미늄(Al)과 백금(Pt)을 증착하여 저항성 전극 및 투명한 schottky 전극을 형성한 평면형 자외선 수광소자를 제작하였다. 제작된 소자에 대해 전기적 특성과 광학적 특성을 조사하여 자외선 센서로서의 적합성을 검토하였다. 사파이어 기판위에 성장된 GaN 박막은 $7.8{\times}10^{16}cm^{-3}$의 도핑(doping)농도와 $138 cm^2/V{\cdot}s$의 이동도(mobility)를 가졌으며, 파장이 365 nm 이하인 빛만을 흡수하는 자외선 감지막 특성을 나타내었다. 5 V의 역방향 전압을 인가하였을 때 제조된 schottky형 자외선 센서는 325 nm의 자외선 파장에서 응답도가 2.84 A/W였고, $4{\times}10^4$의 큰 신호대 잡음비(SNR)의 $3.5{\times}10^9$W의 잡음등가전력(NEP)을 나타내었다. 따라서 이들 결과로부터 GuN를 이용한 schottky 다이오드가 가시광 차단 UV photodetector를 제조할 수 있음을 확인하였다.

• 한국정보통신학회논문지
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• 제14권3호
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• pp.691-698
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• 2010

본 연구에서는 RF magnetron sputtering 법으로 AZO 세라믹 타켓 ($Al_2O_3$ : 3 wt%)을 이용하여 Eagle 2000 유리 기판위에 기판온도 ($100{\sim}500^{\circ}C$)와 공정압력 (10 ~ 40 mTorr)에 따른 AZO 박막을 제작하여, 결정화 특성과 전기적 및 광학적 특성을 조사하였다. 모든 AZO 박막은 육방정계구조를 가지는 다결정 이었고, (002)우선 배향성이 관찰되었다. 기판온도 $300^{\circ}C$, 10 mTorr에서 제작한 AZO 막에서 가장 우수한 (002) 배향성을 나타냈으며, 이때의 반가폭 값은 $0.42^{\circ}$였다. 전기적 특성은 기판온도 $300^{\circ}C$, 10 mTorr에서 가장 낮은 비저항 $2.64{\times}10^{-3}\;{\Omega}cm$과 우수한 캐리어 농도 및 이동도를 $5.29{\times}10^{20}\;cm^{-3}$, $6.23\;cm^2/Vs$를 나타내었다. 모든 AZO 박막은 가시광 영역에서 80%의 투과율을 나타내었으며, 기판온도 증가와 공정압력 감소에 따른 Al 도핑효과의 증가로 밴드 갭이 넓어지는 Burstein-Moss 효과가 관찰 되었다.

• 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.

• 전자공학회논문지 IE
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• 제45권1호
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• pp.1-6
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• 2008

본 연구에서는 발광층에 2 파장 재료를 갖는 백색 유기발광소자를 진공증착법을 사용하여 청색 발광재료인 NPB와 황색 발광재료인 Rubrene을 사용하여 제작하였다. 제작된 소자는 ITO/NPB$(200{\AA})$NPB:Rubrene$(300{\AA})$/BCP$(100{\AA})/Alq_3(100{\AA})/Al(1000{\AA})$ 구조로 하였고 Rubrene의 도핑농도는 0.75 wt%이었다. 소자의 색좌표값은 인가전압 11 V에서 x = 0.3327, y = 0.3387 로 NTSC 색좌표 순수한 백색영역(x = 0.3333, y = 0.3333)에 근접한 순수한 백색에 가까운 값을 얻었고, 이 때 최대발광파장은 560 nm이었다. 소자의 동작 개시전압은 1 V이하이고 발광 개시전압은 4 V이다. 최대 외부양자효율은 인가전압 18.5 V, 전류밑도 $369mA/cm^2$ 일 때 0.457 %를 얻었다.

• 한국세라믹학회지
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• 제31권7호
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• pp.695-702
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• 1994

Current study was undertaken to explain the structural evolution and corresponding changes in the properties of calcium aluminate glasses with the variation of SiO2 doping concentration. Calcium aluminate glasses in the compositional ranges of (100-x)(0.6CaO+0.4Al2O3)+xSiO2(where x=0~60) were fabricated. DTA analysis confirmed an anomalous behavior in glass transition temperature (Tg) with the maximum of 887$^{\circ}C$ and minimum of 859$^{\circ}C$ when x=5 and 50, respectively. densities and refractive indices monotonically decreased with increasing SiO2 content and IR transmitting cutoff shifted to shorter wavelength side when the amount of added SiO2 exceeded 5 mole%. IR fundamental vibration absorption peaks showed the change that NBOs were inclined to SiO4 tetrahedron in the low-silica region and NBO per SiO4 tetrahedra changed from 2 to 0 with increasing silica content. Based on the analysis of IR fundamental vibration absorption peaks, the model of the structural change can be proposed in three step: 1) SiO4 scavenged the NBOs located at AlO4-tetrahedra, which resulted in the increased of Tg values, 2) NBOs located in the main network again with a decrease in Tg, and 3) dominated by the decrease in the relative amount of NBOs in the glass system, where Tg re-increased.