ICMCTF2005 Session CP: Symposium C Poster Session

Thursday, May 5, 2005 5:00 PM in Room Town & Country
Thursday Afternoon

Time Period ThP Sessions | Topic C Sessions | Time Periods | Topics | ICMCTF2005 Schedule

CP-1 Fabrication and Characterization of Indium Tin Oxide Film using Paste System
M.-H. Lee, S.-I. Kim, W.S. Seo (Korea Institute of Ceramic Engineering and Technology, South Korea); D.Y. Lee (Daelim College of Technology, South Korea); B.Y. Kim (Incheon University, South Korea); W.-K. Bang (Korea Nano Co., LTD, South Korea)
Indium tin oxide (ITO) films have found important applications in the opto-electronic devices, conductive AR coatings, heat mirrors and transparent EMI/RFI shielding, due to the prominent properties of them, such as optical transmission and electronic conductivity. For preparation of these films, a number of techniques such as vacuum evaporation, sputtering, etc. have been adopted. Recently, endeavor of process development for them reached to using wet process and much interest has been focused on it. The wet process, using sol-gel or paste, is very useful for the film preparation because films of desired shape and area can be prepared easily and homogeneously without using expensive and complicated equipment. There were many studies about application of paste system in electronic device fields and it was revealed that the final film properties are correlated to a number of factors including thermodynamics and kinetics during burnout and firing, chemical and physical reaction of the powder with the substrate and organic vehicle, powder characteristics and rheological properties of paste. However, there were a few studies using paste system in application of transparent conductive oxide. In this work, ITO paste was prepared by using nano ITO sol and organic vehicle system. ITO sol (solid 30 wt%) was fabricated by milling and mixing 30-50nm ITO powder with ethyl alcohol. Rheological behavior of paste was optimized by controlling organic component. Thin films was deposited on glass substrate, using spin coating and screen printing techniques and treated at various temperatures and N2 gas flow rates. The optimized ITO paste was characterized to show pseudo-plastic behavior and have good wettibility to substrate. The final film was reported as a good transparent electrode because of its high transmission and good conductivity. The relationship with rheological properties and the performance of fired films are discussed through their physical aspects.
CP-2 The Low Temperature Synthesis of Al Doped ZnO Films on Glass & Polymer using Co-Magnetron Sputtering: O2 Effects
Y.M. Chung, C.S. Moon, J.G. Han (Sungkyunkwan University, South Korea)
The greatly increasing use of transparent conducting films for solid-state display devices especially in flat panel display devices has promoted the development of inexpensive materials such as ZnO and SnO2 in place of indium tin oxide (ITO). From the viewpoint that film should be easily etched in order to form fine electrodes, ZnO films are more desirable than SnO2 films. Moreover, by fine control of Al doping contents, it overcomes the weak point of ZnO application at high temperature. But due to the ZnO:Al (ZAO) structural characteristics, it need high temperature process or substrate bias control. Therefore it is limited the transparent electrode application of ZAO on flexible displays. In previous work, we deposited ZAO films on glass and polymer substrate at room temperature with controlling working pressure and obtained the minimum resistivity 8 x 10-4 Ω cm and transparency more than 80 %. In this work, for synthesis of highly conductive and transparent ZAO film, it was deposited by reactive pulsed co-magnetron sputtering onto glass and polymer substrate. By controlling working temperature, oxygen partial pressure and Al concentration, structural, electrical and optical properties of ZAO films were investigated and we obtained the minimum resistivity 7 x 10-4 Ω cm and transparency 90 %.
CP-3 Fabrication and Optical Properties of ZnO Thin Films with Various Orientations and their Nitrogen-Doping Behavior
Y.F. Mei, R.K.Y. Fu, G.G. Siu, P.K. Chu (City University of Hong Kong); Y.C. Lau (General Electric Global Research); H.C. Ong (Chinese University of Hong Kong); C.L. Yang, Z.M. Li, W.K. Ge, Z.K. Tang (Hong Kong University of Science & Technology, Hong Kong)
Zinc oxide, a wide band gap (3.37 eV at room temperature) semiconductor, is a suitable material for short wavelength optoelectronic devices such as light-emitting diodes and lasers in the blue and ultraviolet regions. However, p-type doping of ZnO is not as easy. Nitrogen is regarded to be the more soluble group-V impurity also having the shallowest acceptor level relative to P and As. The doping bottleneck is generally due to intrinsic defects, unintentional hydrogen impurity, and low N solubility. ZnO films can be fabricated using thermal evaporation, metal organic chemical vapor deposition, pulse laser deposition, and molecular beam epitaxy. In this work, a dual plasma technique comprising zinc arc plasma and mixed oxygen and nitrogen gas plasma is used to produce undoped and N-doped ZnO thin film. Undoped ZnO films with various high orientations of (1000), (1100), and (0001) were fabricated under different substrate biases. Some interesting properties of these as-deposited and annealed ZnO films were studied including C-exciton absorption at high energy edge, Raman scattering effect in different crystalline orientation, and photoluminescence (PL) behavior with different intrinsic defects measured at room temperature and low temperature (11K). Our results shows that the ionized zinc atoms and oxygen plasma bond easily and the desirable stoichiometry can be achieved. At the same time, nitrogen can be used to dope the ZnO thin film to optimizing the properties. The stability of N-doping was determined by cathodoluminescence and x-ray photoelectron spectroscopy. Our results reveal unstable Zn-N bonds in the as-deposited N-doped ZnO film and the results are in good agreement with our theoretical calculation aiding our understanding of the N-doping mechanism in ZnO.
CP-4 Electrical Properties of Transparent Conductive Ala-Ga1-a-ZnO Thin Films Prepared by RF Magnetron Sputtering
J.K. Lee, T.H. Kim, I.H. Kim, W.M. Kim (Korea Institute of Science and Technology, South Korea)
Transparent conductive Ala-Ga1-a-ZnO thin films were deposited on glass substrate by RF magnetron sputtering using the ZnO-Al2O3(96-4at%) and ZnO-Ga2O3(99-1at%) targets. The films obtained were polycrystalline with a hexagonal structure and were preferentially oriented in the (0 0 2) crystallographic direction. The mobility and resistivity for the Al:Ga(4:1)at% films were 15cm2/Vsec and 8.2x10-4 ohmcm at 500nm film thickness, respectively. Optical measurements on the films showed that the average transmittance though the visible range was higher than 80%. With this result, we will find the reason why the mobility of ZnO increased abruptly by the changed of Al:Ga concentration and film thickness.
CP-5 Effect of ZnO Addition on Electrical and Structural Properities of SnO2 Thin Films
I.H. Kim (Korea Institute of Science and Technology, South Korea); J.H. Ko, D. Kim (Korea University, South Korea); K.S. Lee, J.-K. Park, T.S. Lee, Y.-J. Baik, B.K. Cheong, W.M. Kim (Korea Institute of Science and Technology, South Korea)
SnO2-ZnO (ZTO) thin films with varying composition of ZnO in the range of 0-20 at.% were prepared by radio frequency (rf) magnetron sputtering, and the crystallization behavior and the corresponding changes in electrical properties upon annealing as well as the electrical and structural properties of the as-deposited ZTO films were investigated. The ZTO films were prepared by co-sputtering of pure ZnO and SnO2 targets without intentional heating, and the content of ZnO was controlled by varying rf power on ZnO target in the range from 0 to 20 W while maintaining rf power on SnO2 target at 42 W. Annealing of ZTO films were performed in air and in vacuum over the temperature range of 200-600 °C. All the as-deposited ZTO films were amorphous, and the crystallization temperature increased with addition of ZnO. Amorphous SnO2 films had low electrical resistivity of 1-2 X 10-3 Ωcm and high optical transparency in the visible range, and were crystallized after annealing at 300 °C and their resistivity increased sharply. Amorphous ZTO films showed the Hall mobility of 15-30 cm2/Vsec and the carrier concentration of 1-20 X 1019 cm-3 with varying ZnO contents, and minimum resistivity of 1-2 X 10-3 Ωcm was obtained. ZTO films with Zn 10 at% kept the amorphous structure even after annealing at 300 °C and their resitivities decreased to one third of those of as-deposited. Discussion was also made on the density of state effective mass and scattering parameter i.e. scattering mechanisms in ZTO films, which were obtained by measuring and analyzing four coefficients (conductivity, Hall, Seebeck and Nernst coefficient) in the temperature range from 100 to 300 K.
CP-6 Effect of AZO Film Depositions on The Photovoltaic Properties of AZO/Cu2O Heterojunction Devices
T. Minami, T. Miyata, K. Ihara, Y. Minamino, S. Tsukada (Kanazawa Institute of Technology, Japan)
Recently, we reported that an energy conversion efficiency over 1% was obtained in heterojunction solar cells that combine an Al-doped ZnO (AZO) thin film with a thick Cu2O sheet. This paper describes the relationship between the film deposition conditions as well as deposition methods and the resulting photovoltaic properties of AZO/Cu2O heterojunction devices fabricated using transparent conducting AZO thin films prepared by various deposition methods. The p-type semiconducting Cu2O sheets (thickness of approximately 0.2 mm), prepared by a heat treatment of copper sheets, functioned as the active layer as well as the substrate in the photovoltaic devices. The n-type semiconducting AZO thin films were deposited by d.c. or r.f. magnetron sputtering, pulsed laser deposition (PLD) or vacuum arc plasma evaporation (VAPE). In magnetron sputtering, Cu2O sheet substrates were placed in various positions relative to the target. One Cu2O substrate was set perpendicular to the target surface, and two were set parallel to the target surface; these positions corresponded to locations opposite the center and the erosion area of the target, respectively. In magnetron sputtering, the obtained photovoltaic properties of the devices fabricated with the perpendicular substrate arrangement were better than those of the devices fabricated with either of the parallel arrangements. The variation in the photovoltaic properties relative to the substrate arrangement may be explained by the resulting interface layer and the extent of damage introduced on the Cu2O surface during the AZO deposition. However, when using AM2 solar illumination, a maximum energy conversion efficiency above 1% was obtained in all devices fabricated with AZO thin films prepared under optimized deposition conditions, irrespective of deposition method. In particular, high efficiencies of 1.6 and 1.5% were obtained in devices fabricated at a substrate temperature around 200°C by PLD and VAPE, respectively.
CP-7 Structural, Optical and Electrical Properties of Li-Doped ZnO Films for the Application of Acoustic Device
B.N. Park, S.H. Jeong, S.-B. Lee, J.-H. Boo (Sungkyunkwan University, South Korea)
Required characteristic of ZnO film is a strong c-axis oriented crystalline structure and high resistivity when used for piezoelectric applications. Lithium doped ZnO (LZO) films were deposited by RF magnetron sputtering method on glass substrate using Li-doped ceramic target of various rate (0 - 10 wt.% LiCl dopant). We investigated a dependency of deposition parameter such as dopant content in target and target to substrate distance (Dts) on structural, optical and electrical properties of the as-grown LZO films by XRD, SEM, UV, 4-point-probe, etc. The LZO films have a highly preferred orientation in the [001] direction. As amount of the Li dopant in the target was increased, the crystallinity was decreased, though the electrical resistivity was increased. Moreover, with increasing Dts the crystallinity and electrical resistivity were increased. When LZO films were sputtered under the deposition condition of room temperature and RF power of 150 W with a target containing less than 2 wt.% content of LiCl at 70 mm of Dts, it showed a strong c-axis orientation as well as high resistivity of above 106 cm.
CP-9 Oxide Films of Multi-Element FeCoNiCrCuAl0.5 Alloy by Reactive DC Sputtering
T.K. Chen, M.S. Wong (National Dong Hwa University, Taiwan)
Using multi-element high-entropy alloy as target in reactive sputtering, oxide films of FeCoNiCrCuAl0.5 were deposited. The evolutions of structure and properties of the resulting films with various oxygen contents were investigated. At low oxygen content, the films transformed to a short-range-order structure from a well crystalline fcc solid solution. At higher oxygen content, a new crystalline oxide phase, matching the XRD pattern of NiCr2O4, was detected and the films became transparent to light. TEM analysis was used to study the structure and composition of the films. UV-Vis absorption spectra of the oxide films show a narrow transmission band that only light with wavelength between 650 nm to 850 nm is allowed to pass. These oxide films exhibit unexpected high hardness, compared with their nitride counterparts, to a value of 20 GPa.
CP-10 Characterizatin of Thermally Evaporated Silver Phthalocyanine Films
R.K. Bedi, H. Gupta (Guru Nanak Dev University, India); A. Mahajan (D. A. V. College, India)
Silver phthalocyanine films have been grown by thermal evaporation technique onto the glass substrates kept at different temperatures in a vacuum of 1.3@sub x@ 10@@super -3@ Pa. The experimental conditions are optimized to obtain better crystallinity of the films. The films so obtained are annealed and studied for electrical and optical characterization. Besides these, the electrical conductivity, carrier concentration and drift mobility of the films are determined in the temperature range 290-400 K. The X-ray diffraction and SEM pattern of these films show crystalline behaviour of films. The films deposited at higher substrate temperature suggest the formation of more ordered and crystalline films. Analysis of optical absorption measurements indicates that interband transition energies of films lie in 1-2 eV. The current-voltage (I-V) characteristics of films show ohmic behaviour of conduction within the investigated field and temperature range (10 - 60 V, 290 - 400 K). The conduction appears to take place by thermally activated hopping mechanism, i.e. hoping between organic macromolecules and/ or between crystallites. The substrate temperature appears to influence the properties of the films. The electrical conductivity, carrier concentration, drift mobility and optical band gap of the films increase with increases in substrate temperature, whereas activation energy, extinction coefficient and refractive index decreases.
CP-11 Spectroscopic Ellipsometry Monitoring of ITO Thin Film Properties Evolution during Amorphous-To-Crystalline Transition
M. Vinnichenko (Kyiv National Taras Shevchenko University, Ukraine and Forschungszentrum Rossendorf, Germany); A. Rogozin (Institute of Ion Beam Physics and Materials Research, Germany); N. Shevchenko, A. Kolitsch, U. Kreissig, W. Moeller (Forschungszentrum Rossendorf, Germany)
Annealing of thin films of amorphous indium tin oxide (ITO) in vacuum is known to decrease their resistivity. The amorphous-to-crystalline transition is often assumed as the reason for this improvement due to a Sn donor activation, but the physical mechanisms behind the experimental observation are not clear. In present work, the films were studied during heating in vacuum within the temperature range Ta=20-330 °C at a constant rate of 5 °C/min as well as at isothermal annealing at Ta=210 °C. This study is focused on in situ spectroscopic ellipsometry (SE) monitoring of the film properties during annealing. In addition, the films were investigated by in situ four point probe resistivity measurement technique and the in situ X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA). The observed temperature dependences of the ellipsometry parameters and resistivity indicate several stages with features at Ta=110, 150, 280, and 310 °C, in contrast to the more simple two-stage behavior of these characteristics obtained during isothermal annealing. Even in the XRD-amorphous state, the film resistivity significantly decreases with increasing temperature due to a free-electron density enhancement as shown by SE. It is likely caused by the generation of oxygen vacancies, because ERDA showed decrease of the oxygen content in the film on this stage of annealing. A rapid crystallization within the temperature range of 250-280 °C leads to a further decrease of the resistivity due to Sn donor activation. The amorphous-to-crystalline transition is accompanied by a film roughening as it is shown by in situ SE and corroborated by atomic force microscopy.
Time Period ThP Sessions | Topic C Sessions | Time Periods | Topics | ICMCTF2005 Schedule