• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.344-344
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• 2014

Transparent amorphous oxide semiconductors such as a In-Ga-Zn-O (a-IGZO) have advantages for large area electronic devices; e.g., uniform deposition at a large area, optical transparency, a smooth surface, and large electron mobility >10 cm2/Vs, which is more than an order of magnitude larger than that of hydrogen amorphous silicon (a-Si;H).1) Thin film transistors (TFTs) that employ amorphous oxide semiconductors such as ZnO, In-Ga-Zn-O, or Hf-In-Zn-O (HIZO) are currently subject of intensive study owing to their high potential for application in flat panel displays. The device fabrication process involves a series of thin film deposition and photolithographic patterning steps. In order to minimize contamination, the substrates usually undergo a cleaning procedure using deionized water, before and after the growth of thin films by sputtering methods. The devices structure were fabricated top-contact gate TFTs using the a-IGZO films on the plastic substrates. The channel width and length were 80 and 20 um, respectively. The source and drain electrode regions were defined by photolithography and wet etching process. The electrodes consisting of Ti(15 nm)/Al(120 nm)/Ti(15nm) trilayers were deposited by direct current sputtering. The 30 nm thickness active IGZO layer deposited by rf magnetron sputtering at room temperature. The deposition condition is as follows: a rf power 200 W, a pressure of 5 mtorr, 10% of oxygen [O2/(O2+Ar)=0.1], and room temperature. A 9-nm-thick Al2O3 layer was formed as a first, third gate insulator by ALD deposition. A 290-nm-thick SS6908 organic dielectrics formed as second gate insulator by spin-coating. The schematic structure of the IGZO TFT is top gate contact geometry device structure for typical TFTs fabricated in this study. Drain current (IDS) versus drain-source voltage (VDS) output characteristics curve of a IGZO TFTs fabricated using the 3-layer gate insulator on a plastic substrate and log(IDS)-gate voltage (VG) characteristics for typical IGZO TFTs. The TFTs device has a channel width (W) of $80{\mu}m$ and a channel length (L) of $20{\mu}m$. The IDS-VDS curves showed well-defined transistor characteristics with saturation effects at VG>-10 V and VDS>-20 V for the inkjet printing IGZO device. The carrier charge mobility was determined to be 15.18 cm^2 V-1s-1 with FET threshold voltage of -3 V and on/off current ratio 10^9.

• Korean Journal of Optics and Photonics
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• v.8 no.6
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• pp.445-449
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• 1997

The complex refractive indices of $Ge_2Se_2Te_5$ which show reversible phase change between the crystalline phase and an amorphous one depending upon the annealing process have been determined in the spectral range of 0.7-4.5 eV. The $Ge_2Se_2Te_5$ films were DC sputter deposited on the crystalline silicon substrate. The spectro-ellipsometry data of a thick film were analyzed following the modelling procedure where the quantum mechanical dispersion relation were used for the complex refractive indices of both the cryastalline phase $Ge_2Se_2Te_5$ and and amorphous phase $Ge_2Se_2Te_5$, respectively. On the other hand, with the surface micro-roughness layer whose effective thickness was determined from AFM analysis, the spectro-ellipsometry data were numerically inverted to yield the complex refractive index of $Ge_2Se_2Te_5$ at each wavelength. With these set of complex refractive indices, the reflectance spectra were calculated and those spectra obtained from the numerical inversion showed better agreement with the experimental reflection spectra for both the cryastalline phase and an amorphous phase. Finally, the thin $Ge_2Se_2Te_5$ film which has the optimum thickness of 26 nm as the medium for optical recording was also analyzed and the quantitative result of the film thickness and the surface microroughness has been reported.

• Korean Journal of Materials Research
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• v.6 no.3
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• pp.309-317
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• 1996

세가지 다른 방법을 이용하여 형성시킨 비정질 실리콘(SiH4 a-Si, Si2H6 a-Si, Si+ implanted SiH4 a-Si)들에 대한 저온 결정화 기구의 차이를 고전적 이론인 Avrami 식(X=1-exptn, X=결정화 분율, t=열처리 시간, n=지수)을 이용하여 검토하였다. Silane으로 형성된 비정질 실리콘의 결정화 과정에서는 Avrami 식에서의 n의 값이 2.0을 나타내고 있어, 결정성장이 이차원적으로 이루어지면서 핵생성률이 시간에 따라 감소하고 있음을 알 수가 있었다. Si+ 이온 주입에 의하여 형성된 비정질 실리콘의 결정화에서는 3.0의 지수 값이 얻어지고 있어, 정상상태의 핵생성과 함께 2차원적인 결정 성장이 이루어지고 있었다. Disilane으로 형성된 비정질 실리콘에 대한 결정화에서는 2.8의 지수값이 얻어져, 정상상태의 핵 생성이 우세하게 일어나는 2차원적인 결정성장이 일어나고 있음을 알 수 있었다. 또한 TEM을 이용하여 시간에 따라 변하는 핵생성률을 조사하여, Avrami 식의 적용이 타당성 있음을 증명하였다. 마지막으로, 최종 입자의 크기가 열처리 온도에 크게 영향을 받고 있지 않음을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.242-242
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• 2012

Transparent oxide semiconductors are increasingly becoming one of good candidates for high efficient channel materials of thin film transistors (TFTs) in large-area display industries. Compare to the conventional hydrogenated amorphous silicon channel layers, solution processed ZnO-TFTs can be simply fabricated at low temperature by just using a spin coating method without vacuum deposition, thus providing low manufacturing cost. Furthermore, solution based oxide TFT exhibits excellent transparency and enables to apply flexible devices. For this reason, this process has been attracting much attention as one fabrication method for oxide channel layer in thin-film transistors (TFTs). But, poor electrical characteristic of these solution based oxide materials still remains one of issuable problems due to oxygen vacancy formed by breaking weak chemical bonds during fabrication. These electrical properties are expected due to the generation of a large number of conducting carriers, resulting in huge electron scattering effect. Therefore, we study a novel technique to effectively improve the electron mobility by applying environmental annealing treatments with various gases to the solution based Li-doped ZnO TFTs. This technique was systematically designed to vary a different lithium ratio in order to confirm the electrical tendency of Li-doped ZnO TFTs. The observations of Scanning Electron Microscopy, Atomic Force Microscopy, and X-ray Photoelectron Spectroscopy were performed to investigate structural properties and elemental composition of our samples. In addition, I-V characteristics were carried out by using Keithley 4,200-Semiconductor Characterization System (4,200-SCS) with 4-probe system.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.72.1-72.1
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• 2010

Thin film a-Si solar cells deposited by PECVD have many advantages compared to the traditional crystalline Si solar cells. They do not require expensive Si wafer, the process temperature is relatively low, possibility of scaling up for mass production, etc. In order to produce thin film solar cells, understanding the relationship between the material characteristics and deposition conditions is important. It has been reported by many groups that the band gap of the a-Si material and the deposition rate has an linear relationship, when RF power is used to control both. However, when the process pressure is changed in order to control the deposition rate and the band gap, a diversion from the well known linear relationship occurs. Here, we explain this diversion by the deposition condition crossing different plasma regions in the Paschen curve with a simple model. This model will become a guide to which condition a-Si thin films must be fabricated in order to get a high quality film.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.295-295
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• 2016

Recently, TCO films with low carrier concentration, high mobility and high work function are proposed beneficial as front electrode in HIT solar cell due to free-carrier absorption in NIR wavelength region and low Schottky barrier height in the front TCO/a-Si:H(p) interface. We report high transmittance and work function zirconium-doped indium tin oxide (ITO:Zr) films with various plasma (Ar/O2 and Ar) conditions. The role of (Ar/O2) plasma was to enhance the work function of the ITO:Zr films whereas the pure Ar plasma based ITO:Zr showed good electrical properties. The RF magnetron sputtered ITO:Zr films with low resistivity and high transmittance were employed as front electrode in HIT solar cells, yield the best performance of 18.15% with an open-circuit voltage of 710 eV and current density of 34.63 mA/cm2. The high work function ITO:Zr films can be used to modify the front barrier height of HIT solar cell.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.296-296
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• 2016

ITO films doped with a small amount of high-permittivity materials not only retain the basic properties of ITO films but also improve some of their properties. We report the highly conductive and transparent (ITO:Zr) films with various substrate (RT to 300oC) temperatures on glass substrate for the HIT solar cell applications. We observed a decrease in sheet resistance from 36 to $11.8{\Omega}/{\Box}$ with the increasing substrate temperature from RT to 300oC, respectively. The ITO:Zr films showed also lowest resistivity of $1.38{\times}10-4{\Omega}.cm$ and high mobility of 42.37cm-3, respectively. The surface and grain boundaries are improved with the increase of substrate temperature as shown by SEM and AFM surface morphologies. The highly conductive and transparent ITO:Zr films were employed as front electrode in HIT solar cell and the best performance of device was found to be Voc = 710 mV, Jsc = 33.70 mA/cm2, FF = 0.742, ${\eta}=17.76%$ at the substrate temperature of $200^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.340-340
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• 2016

We have prepared alumina (Al2O3) doped zinc oxide (AZO) films by DC magnetron sputtering (MS) technique and obtained higher self surface texturing at a high target angle (f). We have characterized the films and applied it as a front electrode of a single junction amorphous silicon solar cell. At a lower f the deposited films show higher values of optical gap (Eg), charge carriers mobility & concentration, crystallite grain size and wider wavelength range of transmission. At higher target angle the sheet resistance, surface roughness, haze factor etc for the films increase. For f=72.5o the haze factor for diffused transmission becomes 6.46% at 540 nm wavelength. At f=72.5o the material shows a reduction in crystallinity and evolution of a hemispherical-type sub-micron surface textures. A Monte Carlo method (MCM) of simulation of the AZO film deposition shows that such an enhanced self-surface texturing of the films at higher f is possible.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.101.2-101.2
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• 2015

급속한 산업화로 인하여 에너지 부족 문제가 대두되고 있는 가운데 에너지 저감 기술의 개발이 요구되고 있다. 국내 반도체 공정의 배기계통에서 소비되는 에너지는 전체 공정에 소비되는 에너지중 상당량에 달하며 10%의 에너지 절감은 연간 1000억원 이상의 비용절감 효과를 기대할 수 있다. 반도체 공정 배기계통은 진공펌프의 특성, 챔버의 부피, 도관의 구조(직경, 길이, 형상), 진공재료의 기체방출 등 여러 가지 요소의 복합적인 영향으로 그 상태가 달라지므로 보다 효과적인 공정의 운용과 에너지 절감을 위해 반도체 공정의 복합 상태 진단기술 개발이 요구되고 있으며 그중 큰 비중을 차지하는 드라이펌프의 실시간 모니터링 기술의 개발이 시급하다. 본 연구에서는 반도체 공정의 복합 상태 진단기술 개발에 대한 기초 연구로서 반도체 공정 배기계통의 conductance 및 유량 변화에 대한 드라이펌프의 특성을 이론적 계산으로 얻어진 결과와 실험을 통하여 얻어진 결과를 비교, 분석하였다. 진공펌프의 기본 특성은 한국표준과학연구원에서 국제규격에 따라 도달진공도, 배기속도, 소비전력, gas load, 소음, 진동 등을 분석하였고, 나노종합기술원의 PECVD 장비(chamber A: amorphous silicon 및 loadlock chamber)에 챔버의 부피, 도관의 구조, 공정가스의 유량 등을 측정하여 simulation 하였으며, 실제 측정값은 LabVIEW 프로그래밍으로 자동화 된 MFC를 이용하여 실제 공정 상태를 모사하였다. 실험은 PECVD의 특성을 고려하여 질소분위기에서 CDG (Capacitance Diaphragm Gauge)를 사용하였다.