• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.309-309
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• 2009

In-Ga-Zn-O (IGZO) has drawn much attention as a compatible material for transparent thin film transistors (TTFT) channel layer due to its high mobility and optical transparency at low processing temperatures. In this work, we investigated the effect of oxygen ambient on structural, electrical and optical properties of amorphous In-Ga-Zn-O (IGZO) thin films by using pulsed laser deposition (PLD). The films were deposited at various oxygen pressures and the structural, electrical and optical properties were investigated. X-ray diffraction (XRD) analysis showed that amorphous IGZO films were grown at all oxygen pressures. The surface morphology and optical properties with various oxygen pressures were studied by field emission scanning electron microscopy (FE-SEM) and UV-VIS spectroscopy, respectively. The grain boundary was observed more apparently and the calculated optical band gap became larger as oxygen pressure increased. To examine the electrical properties, Hall-effect measurements were carried out. The films showed high mobility.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1208-1211
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• 2008

We study the amorphous In-Ga-Zn-O thin-film transistors (TFTs) properties under monochromatic illumination ($\lambda=420nm$) with different intensity. TFT off-state drain current ($I_{DS_off}$) was found to increase with the light intensity while field effect mobility ($\mu_{eff}$) is almost unchanged; only small change was observed for sub-threshold swing (S). Due to photo-generated charge trapping, a negative threshold voltage ($V_{th}$) shift is also observed. The photofield-effect analysis suggests a highly efficient UV photocurrent conversion in a-IGZO TFT. Finally, a-IGZO mid-gap density-of-states (DOS) was extracted and is more than an order lower than reported value for a-Si:H, which can explain a good switching properties of the a-IGZO TFTs.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.134-134
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• 2010

Ga-In-Zn-O 물질은 비정질상태에서 높은 전하 운동성을 가지고 있으며 차세대 투명전극 thin film transistor 대안 소재로 각광받고 있다. 그런데 이 물질은 ion sputtering에 따라 전기적인 특성에 큰 변화가 관찰되고 있으며, 이는 표면에서의 화학적 상태가 전기적 특성을 좌우할 것이라는 것을 의미한다. 또한 보다 안정적이고 신뢰적인 소자를 구현하기 위해서는 ion sputtering에 의한 표면에서의 화학적 특성 변화를 이해하는 것이 매우 중요하다는 것을 의미한다. 본 연구에서는 $Ga_2O_3:In_2O_3$:ZnO의 비율이 각각 1:1:1, 2:2:1, 3:2:1 그리고 4:2:1인 시료를 $Ne^+$이온을 이용하여 sputtering하면서 표면에 민감한 분광분석 기법인 x-ray photoelectron spectroscopy와 x-ray absorption spectroscopy를 이용하여 분광정보의 변화들을 연구하였다. 실험에 의하면, Ga 3d의 양에 비해서 In 4d, Zn 3d의 양은 sputtering 시간에 따라서 각 각 양이 줄어들었으며, 전체적으로 보다 산화가가 높은 경향을 보였으며, valence band maximum 근처에 subgap state를 형성하는 것을 관찰하였다. 또한 sputtering을 계속하는 경우 In 3d, In 4d, 및 Fermi energy 근처에 metallic state가 형성되는 것을 관찰하였다. 이러한 subgap state와 metallic state의 관측은 각기 sputtering에 따라서, 아직 명확하지는 않지만, surface state의 형성 및/혹은 oxygen interstitial의 형성 그리고 metallic In의 형성 및/혹은 oxygen defect의 형성이 이루어지는 것을 의미한다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.576-581
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• 2023

The Ga₂O₃ thin films were deposited using an RF sputtering system and the effect of crystallographic and optical properties under rapid thermal annealing conditions on Ga₂O₃ thin film was evaluated. A rapid thermal annealing method can fabricate a crystalline Ga₂O₃ thin film which is applied to various fields with a low cost and a high efficiency compared with the conventional post-annealing method. In this study, the Ga₂O₃ treated at 900℃ for 1 min showed the beta and gamma phases in XRD measurement. In optical properties, the crystalline Ga₂O₃ represented a high transmittance of more than 80% in the visible region and was calculated with a high optical bandgap energy of 4.58 eV. The beta and gamma phases Ga₂O₃ can be obtained by adjusting the rapid thermal annealing temperatures, and the various properties such as the optical bandgap energy can be controlled. Moreover, it is expected that crystalline Ga₂O₃ can be applied to various devices by controlling not only temperature but process time.

• Electrical & Electronic Materials
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• v.7 no.2
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• pp.100-106
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• 1994

A bilayer film consisting of a layer of a-Se$_{75}$ Ge$_{25}$ with a surface layer of silver -100[.angs.] thick and a monolayer film of a-Se$_{75}$ Ge$_{25}$ are irradiated with 9[keV] Ga$^{+}$ ion beam. The Ga$^{+}$ ion (10$^{16}$ [ions/cm$^{2}$] exposed a-Se$_{75}$ Ge$_{25}$ and Ag/a-Se$_{75}$ Ge$_{25}$ thin films show an increase in optical absorption, and the absorption edge on irradiation with shifts toward longer wavelength. The shift toward longer wavelength called a "darkening effect" is observed also in film exposure to optical radiation(4.5*10$^{20}$ [photons/cm$^{2}$]). The 0.3[eV] edge shift for ion irradiation films is about twice to that obtained on irradiation with photons. These large changes are primarily due to structural changes, which lead to high etch selectivity and high sensitivity.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.89-89
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• 2011

a-GIZO(비정질 Ga-In-Zn-O)박막은 유연하며 광학적으로 투명하고 높은 전자의 이동도를 갖는 반도체적 특성을 갖기 때문에 차세대 display분야에서 TFT(Thin-Film-Transistor)의 high speed active-matrix layer로써 각광을 받고 있다. 이 물질의 표면은 환경 및 표면처리에 매우 민감하며 [1,2], 이 표면에 metal이 증착되는 경우에도, 선행 연구에 의하면, 다양한 chemical state가 나타남을 알 수 있었다. 이것은 metal의 증착에 따라 metal과 a-GIZO 사이의 contact 저항이 달라짐을 의미한다. 우리는 a-GIZO 박막 위에 Au를 단계적으로 증착시키면서, Au coverage 증가에 따른 core-level과 valence에서의 x-ray photoelectron spectra의 변화를 살펴봄으로써 a-GIZO박막과 Au의 계면에서 일어나는 chemical state의 변화를 알 수 있었다. 특히, Au deposition의 전 처리과정으로써 Ne ion sputtering을 두 단계로 다르게 하여 a-GIZO의 표면환경에 따른 Au 증착의 영향을 살펴보았다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.85.2-85.2
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• 2010

$Cu_2ZnSnSe_4$ (CZTSe) is one of candidate to alternate $Cu(In,Ga)Se_2$ as solar absorber material for solar cell. The expensive elements of In and Ga are replaced by Zn and Sn, respectively to lower the material cost. In this study we fabricated CZTSe thin film by selenization of single precursor layer consisted metallic constituent. Precursor compositions ratio were selected to have Cu-poor and Zn-rich content and prepared by RF magnetron sputtering. Thermal processing was applied to introduce selenium into as-deposited films at temperatures ranging from 350 to 500 for time up to 120 minutes. Single precursor films showed amorphous structure and consist of individual elements of Cu, Zn, and Sn. It was confirmed by XRD analysis that synthesis of CZTSe compound is occurred from lower temperature process, although concurrently additional phases such as binary cooper selenides are also existed. The quality of CZTSe crystal was improved as temperature increased. We also investigated the optical and electrical properties of as-selenized CZTSe as well.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.10
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• pp.620-624
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• 2015

We have studied structural, optical and electrical properties of In-Ga-doped ZnO (IGZO) thin films. The IGZO thin films were deposited on the corning 1737 glass by RF magnetron sputtering method. The RF power in sputtering process was varied as 30, 50, 70, and 90 W respectively. All of the IGZO thin films transmittance in the visible range (400 nm ~ 800 nm) was above 83%. XRD analysis showed the IGZO thin films amorphous structure of the thin films without any peak. And also IGZO thin film have low resistivity ($1.99{\times}10^{-3}{\Omega}cm$), high carrier concentration ($6.4{\times}10^{20}cm^{-3}$), and mobility ($10.3cm^2V^{-1}s^{-1}$). By the studies we found that IGZO transparent thin film can be used as optoelectronic material and introduced application possibility for future electronic devices.

• Electronic Materials Letters
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• v.14 no.6
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• pp.749-754
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• 2018

Previous studies have reported on the mechanical robustness and chemical stability of flexible amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) on plastic substrates both in flat and curved states. In this study, we investigate how the polyimide (PI) substrate affects hydrogen concentration in the a-IGZO layer, which subsequently influences the device performance and stability under bias-temperature-stress. Hydrogen increases the carrier concentration in the active layer, but it also electrically deactivates intrinsic defects depending on its concentration. The influence of hydrogen varies between the TFTs fabricated on a glass substrate to those on a PI substrate. Hydrogen concentration is 5% lower in devices on a PI substrate after annealing, which increases the hysteresis characteristics from 0.22 to 0.55 V and also the threshold voltage shift under positive bias temperature stress by 2 ${\times}$ compared to the devices on a glass substrate. Hence, the analysis and control of hydrogen flux is crucial to maintaining good device performance and stability of a-IGZO TFTs.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.1
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• pp.82-89
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• 2017

In this work, InGaZnO thin film transistors with Ni, Al and ITO source and drain electrode materials were fabricated to analyze a hot carrier induced device degradation according to the electrode materials. From the electrical measurement results with electrode materials, Ni device shows the best electrical performances in terms of mobility, subthreshold swing, and $I_{ON}/I_{OFF}$. From the measurement results on the device degradation with source and drain electrode materials, Al device shows the worst device degradation. The threshold voltage shifts with different channel widths and stress drain voltages were measured to analyze a hot carrier induced device degradation mechanism. Hot carrier induced device degradation became more significant with increase of channel widths and stress drain voltages. From the results, we found that a hot carrier induced device degradation in InGaZnO thin film transistors was occurred with a combination of large channel electric field and Joule heating effects.