• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.312.1-312.1
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• 2014

Chalcopyrite계 화합물 반도체인 $Cu(InGa)Se_2$ (CIGS)는 직접천이형 에너지 밴드갭과 전파장 영역에 대하여 높은 광흡수계수($1{\times}$[10]^5/cm)를 가지므로 두께 $1{\sim}2{\mu}m$인 박막형태으로 고효율의 태양전지 제조가 가능하다. 또한, 박막공정의 저가 가능성을 나타내면서 전세계적으로 많은 연구와 관심을 받고 있고, 현재 상용화되어 있는 결정질실리콘 태양전지를 대체할만한 재료로 주목 받고 있다. 일반적으로, CIGS박막형 태양전지 구성은는 유리를 기판으로 하여 5개의 단위 박막인 Mo 후면전극, p형 반도체 CIGS 광흡수층, n형 반도체 CdS 버퍼층, doped-ZnO 상부 투명전극, $MgF_2$ 반사방지막으로 이루어진다. 이들 중에서 태양전지의 에너지 변환효율에 결정적인 영향을 미치는 구성된다. CIGS 광흡수층의 제조는 크게 진공법과 비진공방법으로 나뉜다. 현재까지 보고된 문헌에 따르면 CIGS 박막형 태양전지의 경우에 동시증발법으로 20.3%의 에너지 변환효율을 보였지만,는데, 이는 진공장비 특성상 공정단가가 높고 대면적화가 어렵다는 단점을 가진다. 따라서, 비진공법을 이용하여 광흡수층 제작하는 것이 기술적으로 진보할 여지가 크다고 볼 수 있다. 반면 현재 상용화되어 있는 결정질실리콘 태양전지를 대체할만한 방법으로 주목 받고 있는 비진공을 이용한 저가공정은 최근 15.5%의 에너지 변환효율이 보고 되었다. 비진공법에는 전계를 이용한 증착법 및 스프레이법으로 나뉘며, 이들 광흡수층 재료의 화학적 합성은 III족 원소인 In, Ga의 함량비에 따라 광흡수층의 에너지 밴드갭(1.04~1.5 eV) 조절이 가능하다. 따라서, 본 연구에서는 비진공법에 사용되는 CIGS재료의 화학적 합성조건을 변화시켜 III족 원소의 조성비 조절을 시도하였다. CIGS 분말 시료의 입자 형태와 크기를 FE-SEM을 이용하여 관찰하였고, 화합물의 성분비를 EDX 및 XRD 분석을 통해 Ga 함량에 따른 구조적 차이를 비교해 보았다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.398.1-398.1
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• 2014

The $Cu_2ZnSnSe_4$ (CZTSe) thin films solar cell is one of the next generation candidates for photovoltaic materials as the absorber of thin film solar cells because it has optimal bandgap (Eg=1.0eV) and high absorption coefficient of $10^4cm^{-1}$ in the visible length region. More importantly, CZTSe consists of abundant and non-toxic elements, so researches on CZTSe thin film solar cells have been increasing significantly in recent years. CZTSe thin film has very similar structure and properties with the CIGS thin film by substituting In with Zn and Ga with Sn. In this study, As-deposited CZTSe thin films have been deposited onto soda lime glass (SLG) substrates at different deposition condition using Pulsed Laser Deposition (PLD) technique without post-annealing process. The effects of deposition conditions (deposition time, deposition temperature) onto the structural, compositional and optical properties of CZTSe thin films have been investigated, without experiencing selenization process. The XRD pattern shows that quaternary CZTSe films with a stannite single phase. The existence of (112), (204), (312), (008), (316) peaks indicates all films grew and crystallized as a stannite-type structure, which is in a good agreement with the diffraction pattern of CZTSe single crystal. All the films were observed to be polycrystalline in nature with a high (112) predominant orientation at $2{\theta}{\sim}26.8^{\circ}$. The carrier concentration, mobility, resistivity and optical band gap of CZTSe thin films depending on the deposition conditions. Average energy band gap of the CZTSe thin films is about 1.3 eV.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.103-104
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• 2008

In this paper we report upon an investigation into the effect of DC bias voltage on the electrical and optical properties of Gallium doped zinc oxide (GZO) film. GZO films were deposited on glass substrate without substrate temperature by RF magnetron sputtering from a ZnO target mixed with 5 wt% $Ga_2O_3$. we investigated sample properties of bias voltage change in 0 to -60 V. We were able to achieve as low as $5.89\times10^{-4}$ ${\Omega}cm$ and transmittance over 87%. without substrate temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.239.1-239.1
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• 2014

최근 산화아연이나 산화주석을 기반으로 한 산화물 박막 트랜지스터의 연구가 활발히 진행되고 있다. 2004년 일본의 Hosono 교수 그룹에서 비정질 InGaZnO (IGZO) 박막을 이용한 TFT소자 제작을 발표하고 우수한 특성을 확인한 후 산화물 TFT 소자기술에 대한 전 세계적인 연구개발의 계기가 마련 되었다. 그러나 다성분계 화합물 산화물 반도체의 경우 복잡한 성분 조합과 조절이 어렵고, 공정의 제약으로 인해 상용화에 어려움을 겪고 있다. 산화아연의 경우 증착공정중 쉽게 결정화가 이뤄져 대면적화가 어렵고, 결정립계에 의한 이동도 저하, DC 신뢰성 저하가 발생한다. 이에 비해 산화 티타늄의 경우 증착과정후 열처리를 통해서 비정질상과 결정립상을 조절할 수 있다. 하지만, 현재까지 발표된 산화 티타늄 기반의 박막 트랜지스터의 경우 내부 캐리어의 조절이 상대적으로 어려운 단점이 있었다. 본 연구에서는 산화 티타늄기반의 박막 트랜지스터를 제작하고 공정중 산소 분압을 조절하여 소자 특성을 개선시키고 동작모드를 조절하는 연구를 진행하였다. Bottom gate 형식의 $TiO_2$ TFT를 제작하였고 전이 특성을 살펴본 결과 산소분압이 증가할수록 이동도는 감소하는 경향이 나타났다. 또한, 산소분압을 조절하여 박막 내부의 캐리어를 조절할 수 있는 가능성을 보였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.5
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• pp.373-376
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• 2009

In this paper we report upon an investigation into the effect of DC bias voltage on the electrical and optical properties of Gallium doped zinc oxide (GZO) film. GZO films were deposited on glass substrate without substrate temperature by RF magnetron sputtering from a ZnO target mixed with 5 wt% $Ga_{2}O_{3}$. we investigated sample properties of bias voltage change in 0 to -60 V. We were able to achieve as low as $5.89{\times}10^{-4}{\Omega}cm$ and transmittance over 88 %. without substrate heating.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.693-696
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• 2011

Recently, amorphous oxide semiconductors (AOSs) based thin-film transistors (TFTs) have received considerable attention for application in the next generation displays industry. The research trends of AOSs based TFTs investigation have focused on the high device performance. The electrical properties of the TFTs are influenced by trap density. In particular, the threshold voltage ($V_{th}$) and subthreshold swing (SS) essentially depend on the semiconductor/gate-insulator interface trap. In this article, we investigated the effects of Ar plasma-treated $SiO_2$ insulator on the interfacial property and the device performances of amorphous indium gallium zinc oxide (a-IGZO) TFTs. We report on the improvement in interfacial characteristics between a-IGZO channel layer and gate insulator depending on Ar power in plasma process, since the change of treatment power could result in different plasma damage on the interface.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.169-170
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• 2007

In this paper we report upon an investigation into the effect of sputter pressure and RF power on the electrical properties of Gallium doped zinc oxide (GZO) film. GZO films were deposited on glass substrate without substrate temperature by RF magnetron sputtering from a ZnO target mixed with 5 wt% $Ga_2O_3$. Argon gas pressure and RF power were in the range of 1~11 mTorr, and 50~100 W, respectively. However, the resistivity of the film was strongly influenced by the sputter pressure and RF power. We were able to achieve as low as $1.5{\times}10^{-3}\;{\Omega}cm$, without substrate temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.268-268
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• 2016

Chemical sensors have attracted much attention due to their various applications such as agriculture product, cosmetic and pharmaceutical components and clinical control. A conventional chemical and biological sensor is consists of fluorescent dye, optical light sources, and photodetector to quantify the extent of concentration. Such complicated system leads to rising cost and slow response time. Until now, the most contemporary thin film transistors (TFTs) are used in the field of flat panel display technology for switching device. Some papers have reported that an interesting alternative to flat panel display technology is chemical sensor technology. Recent advances in chemical detection study for using TFTs, benefits from overwhelming progress made in organic thin film transistors (OTFTs) electronic, have been studied alternative to current optical detection system. However numerous problems still remain especially the long-term stability and lack of reliability. On the other hand, the utilization of metal oxide transistor technology in chemical sensors is substantially promising owing to many advantages such as outstanding electrical performance, flexible device, and transparency. The top-gate structure transistor indicated long-term atmosphere stability and reliability because insulator layer is deposited on the top of semiconductor layer, as an effective mechanical and chemical protection. We report on the fabrication of InGaZnO TFTs with silver nanowire as the top gate electrode for the aim of chemical materials detection by monitoring change of electrical properties. We demonstrated that the improved sensitivity characteristics are related to the employment of a unique combination of nano materials. The silver nanowire top-gate InGaZnO TFTs used in this study features the following advantages: i) high sensitivity, ii) long-term stability in atmosphere and buffer solution iii) no necessary additional electrode and iv) simple fabrication process by spray.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.169-169
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• 2010

As display industry requires various applications for future display technology, which can guarantees high level of flexibility and transparency on display panel, oxide semiconductor materials are regarded as one of the best candidates. $InGaZnO_4$(IGZO) has gathered much attention as a post-transition metal oxide used in active layer in thin-film transistor. Due to its high mobility fabricated at low temperature fabrication process, which is proper for application to display backplanes and use in flexible and/or transparent electronics. Electrical performance of amorphous oxide semiconductors depends on the resistance of the interface between source/drain metal contact and active layer. It is also affected by sheet resistance on IGZO thin film. Controlling contact/sheet resistance has been a hot issue for improving electrical properties of AOS(Amorphous oxide semiconductor). To overcome this problem, post-annealing has been introduced. In other words, through post-annealing process, saturation mobility, on/off ratio, drain current of the device all increase. In this research, we studied on the relation between device's resistance and post-annealing temperature. So far as many post-annealing effects have been reported, this research especially analyzed the change of electrical properties by increasing post-annealing temperature. We fabricated 6 main samples. After a-IGZO deposition, Samples were post-annealed in 5 different temperatures; as-deposited, $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$ and $500^{\circ}C$. Metal deposition was done on these samples by using Mo through E-beam evaporation. For analysis, three analysis methods were used; IV-characteristics by probe station, surface roughness by AFM, metal oxidation by FE-SEM. Experimental results say that contact resistance increased because of the metal oxidation on metal contact and rough surface of a-IGZO layer. we can suggest some of the possible solutions to overcome resistance effect for the improvement of TFT electrical performances.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.405-406
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• 2013

Ga-doped ZnO (GZO)는 $300^{\circ}C$ 이상의 온도에서는 전기적으로 불안정하기 때문에 CIGS, CdTe, DSC와 같은 태양전지의 높은 공정온도 때문에 사용이 제한적이다. ZTO thin film은 Al2O3, SiO2, TiO2, ZnO tihin film과 비교하여 산소 및 수분에 대하여 투과성이 상대적으로 낮은 것으로 알려져 있다. 따라서 GZO single layer에 비하여 ZTO-GZO multi-layer를 구성하여 TCO를 제작하면, 높은 공정온도에서도 사용 가능하다. 실제 제작된 GZO single layer (300 nm)에서 비저항이 $7.69{\times}10^{-4}{\Omega}{\cdot}cm$에서 $500^{\circ}C$에서 열처리 후 $7.76{\times}10^{-2}{\Omega}{\cdot}cm$으로 급격하게 상승한다. ZTO single layer (420 nm)는 as-grown에서는 측정 불가했지만, $400^{\circ}C$에서 열처리 후 $3.52{\times}10^{-1}{\Omega}{\cdot}cm$ $500^{\circ}C$에서 열처리 후 $4.10{\times}10^{-1}{\Omega}{\cdot}cm$으로 열처리에 따른 큰 변화가 없다. 또한 ZTO-GZO multi-layer (720 nm)의 경우 비저항이 $2.11{\times}10^{-3}{\Omega}{\cdot}cm$에서 $500^{\circ}C$에서 열처리 후 $3.67{\times}10^{-3}{\Omega}{\cdot}cm$으로 GZO에 비하여 상대적으로 변화폭이 작다. 또한 ZTO의 두께에 따른 영향을 확인하기 위하여 ZTO를 2 scan, 4 scan, 6 scan 공정 진행 및 $500^{\circ}C$에서 열처리 후 ZTO, ZTO-GZO thin film의 비저항을 측정하였다. ZTO의 경우 $3.34{\times}10^{-1}{\Omega}{\cdot}cm$ (2 scan), $3.62{\times}10^{-1}{\Omega}{\cdot}cm$ (4 scan), $4.1{\times}10^{-1}{\Omega}{\cdot}cm$ (6 scan)으로 큰 차이가 없으며, ZTO-GZO에서도 $3.73{\times}10^{-3}{\Omega}{\cdot}cm$ (2 scan), $3.42{\times}10^{-3}{\Omega}{\cdot}cm$ (4 scan), $3.67{\times}10^{-3}{\Omega}{\cdot}cm$ (6 scan)으로 큰 차이가 없음을 확인하였다. 염료감응 태양전지에 적용하여 기존에 사용되는 FTO대신에 ZTO-GZO를 사용하며, 가격적 측면, 성능적 측면에서 개선 가능할 것으로 생각된다.