ICMCTF2004 Session CP: Symposium C Poster Session

Thursday, April 22, 2004 5:00 PM in Room San Diego

Thursday Afternoon

Time Period ThP Sessions | Topic C Sessions | Time Periods | Topics | ICMCTF2004 Schedule

CP-1 Investigation of Nitrogen-doped Zinc Oxide Thin Film Prepared by Dual Plasma Implantation and Deposition
Y.F. Mei, R.K.Y. Fu, G.G. Siu, P.K. Chu (City University of Hong Kong)
Zinc oxide, which is a wide band gap (3.37 eV at room temperature) semiconductor material, is considered as a potential material for short wavelength optoelectronic devices, such as light-emitting diodes and lasers working in ultraviolet and blue light region. However, ZnO has the "asymmetric doping" limitation, in that n-type doping is easily obtained, but it is difficult to dope ZnO into p-type. Nitrogen is believed to be a promising p-type dopant for ZnO. Nitrogen (N) doping in ZnO, which can be fabricated using thermal evaporation, metal organic chemical vapor deposition (MOCVD), pulse laser deposition (PLD), molecular beam epitaxy (MBE), and so on, has been studied to realize p-type conductivity, but low-resistivity and reproducible p-type conductivity is still a great challenge. In this work, a dual plasma technique comprising zinc arc plasma and mixture gas (oxygen and nitrogen) plasma is used to facilitate N-doped ZnO thin film. Chemically, the ionized zinc atoms and oxygen plasma are easily to bond and deposit with desirable stoichiometry. At the same time, dilute ionized nitrogen can be used to dope the ZnO thin film for optimizing the properties. Several deposition parameters such as substrate bias, oxygen and nitrogen flow rate, zinc plasma output and substrate temperature are experimented to synthesize optimal N-doped ZnO film on silicon and quartz substrate. Structure, surface morphology, and optical property, as well as conductivity are studied with a series of thermal treatment.
CP-2 Preparation of Transparent Conducting ITO Film using SnO2 Nanoparticles Dispersed Solution
S.J. Wang, H.H. Park (Yonsei University, South Korea)
The SnO2 nanoparticles-dispersed indium oxide sol was over-coated on the prepared conventional indium tin oxide (ITO) using glass substrate as a substrate to reduce surface Sn ion composition and insufficient transition of SnO-SnO2 and to obtain high work function at the surface of ITO films. SnO2 nanoparticles were fabricated from solution process. The thermal densification and crystallization of the films was carried out using rapid thermal annealing at 600°C. We determined the surface bonding state and work function of surface-modified ITO films on glass substrates using X-ray photoemission spectroscopy, surface morphology using atomic force microscopy, and electrical properties using I-V meter.
CP-3 Photo-detecting using Epitaxial 3C-SiC Films on p-Si
S. Im, J.M. Choi, I.S. Jeong (Yonsei University, South Korea)
Unintentionally doped n-type silicon carbide films (cubicβ-SiC) of ~300 nm thickness were epitaxially grown on p-Si (100) by chemical vapor deposition and then Al electrode was designed to evaporate on the film. Under a photo-illumination range of 200-650 nm (1 mW), our hetero n-p photodiode revealed quite a high responsitivity over 0.2-0.3 A/W. However, the photodiode also shows a high dark-leakage-current under reverse bias conditions. It is probably because there may exist the high density of dislocations and defects in n-SiC/p-Si junction interface. High Resolution Transmission Electron Microscopy (HRTEM) and X-ray diffraction(XRD) results are also discussed in the presentation.
CP-4 Electrical Properties of Nano Cu2O Films Prepared by DC Sputtering
Y.M. Lu, J.Y. Chen, T.S. Wey, I.C. Leu (Kun Shan University of Technology, Taiwan, R.O.C.)
Electrical properties of nano Cu2O films prepared by DC sputtering Cuprous oxide (Cu2O) has been extensively investigated as a candidate for a photovoltaic material. Though practical applications have not been achieved to data because of the difficulty in controlling its electrical properties,Cu2O is still attractive because it is aboundantly available material and has the advantages of high-absorption coefficient, nontoxicity, and low-cost producibility.Cu2O films were deposited by reactive DC-sputtering on barium borosilicate glass (Corning 7059) substrate using a Cu target of 99.99% purity and Ar and oxygen mixture gases. The formation of Cu2O phase is strongly dependent on the oxygen and argon flow ratio. When the flow rate of oxygen is in the range of 3~5ml/min,Cu2O phase form. The grain size of Cu2O increase from 17nm to 40nm as the substrate temperature raises from 100°C to 350°C. The resistivity of Cu2O films decrease with increasing substrate temperature. The minimum resistivity is as low as 126Ω-cm. when the substrate temperature is 350°C. All carrier concentrations are almost kept constant in the rang of 3.0*1015-7.0*1015 cm-3 and the largest value of mobility is 34 cm2/V-S in this study.
CP-5 Ultraviolet Detecting Properties of ZnO-based Thin Film Transistors
S. Im, H.S. Bae (Yonsei University, South Korea)
ZnO-based thin film transistors (TFTs) have been fabricated and their UV-detecting properties were characterized. ZnO films of ~100 nm thickness were deposited as channel layers on SiO2/p-Si substrate by r.f. sputtering at room temperature (RT). For source/drain contacts, Al was evaporated through a shadow mask. The photo-responsivity of our ZnO-based TFTs were measured under photo-illumination of 0.7 mW in both ultra-violet (UV) range of 200-380 nm and visible range. Dark- and photo- current-voltage characteristics for TFTs show that our ZnO-based TFTs are highly sensitive in UV rather than in visible range.
CP-6 Electrical and Optical Properties of TCO-Cu2O Heterojunction Devices
H. Tanaka, T. Shimakawa, T. Miyata, T. Minami (Kanazawa Institute of Technology, Japan)
This report describes the electrical and optical properties of photovoltaic heterojunction devices fabricated by depositing various transparent conducting oxide (TCO) thin films on a Cu2O sheet. N-type semiconducting TCO films such as In2O3, ZnO, ITO, Al-doped ZnO (AZO) and ZnO-In2O3 (ZIO) multicomponent oxides were deposited by pulsed laser deposition (PLD), d.c. magnetron sputtering or r.f. magnetron sputtering. The Cu2O sheets, prepared by the heat treatment of copper sheets (thickness of 0.2 mm), functioned as the active layer as well as the substrate in a device that was a polycrystalline p-type semiconductor with a hole concentration of approximately 4X1014 cm-3. An Au thin film was deposited on the back side of the Cu2O substrate as an ohmic electrode. The obtained voltage-current (V-I) characteristics were dependent on not only the kind of TCO materials used but also the condition and the method of TCO film depositions. For example, for TCO-Cu2O heterojunction devices that were fabricated with TCO films deposited at 150°C by the PLD method, ZnO- and AZO-Cu2O heterojunction devices always exhibited a rectifying characteristic. However, In2O3- and ITO-Cu2O heterojunction devices exhibited an ohmic characteristic. In ((ZnO)1-X-(In2O3)X)- and ((AZO)1-X-(ITO)X)-Cu2O heterojunction devices, increasing the content of In2O3 or ITO, respectively, in the range from 0 to 100 mol.% changed the resulting V-I characteristic from rectifying to ohmic. The photovoltaic properties of the devices described above were measured under AM2 solar illumination. An efficiency (η) of 1.2%, an open circuit voltage (VOC) of 0.41V, a short circuit current density (ISC) of 7.1mA/cm2 and a fill factor (F.F.) of 0.42 were obtained in an AZO-Cu2O heterojunction device. It was found that the values of η, VOC, ISC and F.F. for ((ZnO) 1-X-(In2O3)X)- and ((AZO)1-X-(ITO) X)-Cu2O heterojunction devices decreased as the content of In2O3 or ITO, respectively, was increased. It should be noted that the obtainable photovoltaic properties were considerably affected by the TCO preparation conditions.
CP-7 Infrared Reflectivity of Refractory Metal Films : Dependence on Physical Vapour Deposition Conditions
S. Schelz, J.-L. Longuet, F. Guillet, P. Carles (CEA Le Ripault, France)
Thin refractory metal films have been deposited by either electron beam evaporation or magnetron sputtering using different deposition conditions. Their optical and structural properties have been investigated in detail by means of photo spectrometry, ellipsometry, X-ray diffraction and electron probe micro analysis. The infrared reflectivity of the refractory metal films depends on the deposition technique and on the deposition conditions, as for example substrate temperature, growth rate and base pressure. This dependence has been correlated with the crystalline structure of the coatings, as well as with oxygen impurities incorporated in the growing film. Furthermore, the angular dependence of the reflectivity of thin refractory metal films covered by a protective oxide coating has been studied. The experimental reflectivity data of the deposited films are compared to calculated spectra using optical constants from litterature of the corresponding bulk materials.
CP-8 Interface Formation in Organic Electroluminescence Devices using Various Electrodes
S. Yoon, H.J. Choi, H.H. Park (Yonsei University, South Korea)

Conjugated polymers can serve as the active material in polymer electroluminescent devices. The incorporation of nano-particles in conjugated polymer, a formation of nano-composite, have been increasingly studied because of the enhanced optical electronic properties starting from the characteristics of organic light-emitting diodes (OLEDs) such as high luminescence, low drive voltage, and a variety of emission color. The performance of an OLED is strongly affected not only by the properties of its constituent organic layers but also by the electrodes and the interfaces they form with the carrier-transport layers.

In this study, we focused on interface between metal cathode and active layer. The candidates for the cathode were studied included Al, Ag, Ba, Zn, Cr, and Mg. And we would control interfacial characteristics by tuning composition of Ag-Mg alloy electrode. We used poly (p-phenylene vinylene) (PPV) and PPV/SiO2nano-composite as an active layer. Interfaces were investigated using X-ray photoelectron spectroscopy (XPS). The surface morphology of the structure was observed by atomic force microscopy (AFM) and the optical property was measured using electroluminescence (EL). The effect of the interface on the optoelectronic properties of the structure system was discussed on the point of view of interfacial bonding distribution, which mainly controls the energy state and defect distributions at the interface.

CP-9 Photoluminescence and Nanosecond Lifetimes of Blended Polythiophene Films
V. Teixeira, H.N. Cui (Universidade do Minho, Portugal); Haiwon Lee (Hanyang University, South Korea)
The interest in organic electroluminescence (EL) was revived mainly by Tang and Van Slyke in 1987. Until now one of the interesting candidate polymer for fabricating LEDs (light emitting diode) is polythiophene. Normally its multilayer device can be fabricated by vacuum evaporation method. Now the techniques to form thin films of polymers from solution were given much attention. Here the spin coating has been used to fabricate blend thin films. Blend and doped polymer systems have the unique advantage of simplicity among macromolecular systems. Many enforces have been done to improve the emission efficiency, device stability and different color display by blending polymers. Thin films of the blend luminescent poly 3-(2-(5-chlorobenzotriazolo) ethyl) thiophene (PCBET) with PVK (polyvinylcarzole) were obtained in the different ratios. The energy transfer mechanisms and fluorescence liftetimes of excited state in the blend films were investigated by nanosecond time-resolved spectroscopy, UV-vis and photoluminescence (PL) spectra. The fluorescence lifetime of PCBET film is 1.31 ns (nanosecond). The fluorescence lifetime of PCBET/PVK film (4:6 wt.) is 1.89 ns at 590 nm emission of PCBET, which is between that of PCBET film (1.31 ns) and PVK film (44.01 ns at 430 nm emission). The short lifetime 1.31 ns of PCBET is probably due to aggregated species in the spin coating film of pure luminescent polymer. The data from the concentration effect and energy transfer effect of the sample PCBET/PVK could be fitted with single exponential component. The results and their PL spectra indicate that energy transfer exists from PVK to PCBET.
CP-10 Substrate Pre-treatment for Improvements in Structural and Mechanical Properties of Zinc Oxide Coatings on Glass
G.T. West, P.J. Kelly (University of Salford, United Kingdom)
Reactively sputtered zinc oxide coatings were deposited onto float glass substrates following exposure of the substrates to an oxygen ion beam. A Hall-effect linear ion source was used to produce ion beams at different nominal beam voltages in the range 0-1500 V, within an otherwise standard unbalanced magnetron sputtering system. Coatings were deposited onto the pre-treated glass under identical operating conditions and were then characterised in terms of their structural and mechanical properties. A series of consistent trends were found revealing improvements in these properties with increasing ion beam voltage. For example, a reduction in the surface roughness of the deposited film, as measured via AFM, was observed. Critical load scratch testing and mechanical wear testing demonstrated significant improvements in mechanical durability, with peak values occurring for glass that had been pre-treated with a beam voltage of 1000V. These improvements in structural and mechanical properties were obtained without any effect on the optical properties of these coatings, which were measured via spectrophotometry. XRD analysis of these coatings indicated that they all had a strong (002) texture, but that the position and width of this peak varied with substrate pre-treatment. This work demonstrates the ability to improve film properties through the pre-treatment of substrates with the linear ion source.
CP-11 Determining Ruthenium's Optical Constants in the Extreme Ultraviolet from 11-14 nm
L.J. Bissell, D.D. Allred, R.S Turley (Brigham Young University)
We have measured the indices of refraction of sputtered Ru thin films from 11-14 nm via reflectance and transmission measurements at the Advanced Light Source at Lawrence Berkley National Laboratory. We compare the measured indices to previously reported values, and to the values predicted by the atomic scattering factor (ASF) model. Our measured values agree with the ASF model within a factor of 0.9. We report the measured indices of refraction of Ru, and discuss the potential of Ru capped Mo/Si multilayers for use in extreme ultraviolet lithography.
CP-12 The Effect on Electrical Properties of rf Magnetron Sputtered IZO Thin Films with a Post Deposition Annealing Treatment
C.Y. Chen (National Cheng-Kung University, Taiwan, R.O.C.)
Oxide films in the ZnO-In2O3 system were deposited by radio-frequency sputtering of ZnO and In2O3 targets at substrate temperatures from room temperature up to 250. The effect on composition, texture, lattice parameter, grain size, grain morphology, and surface morphology of IZO thin films were analyzed by x-ray photoelectron spectroscope, x-ray diffraction, transmission electron microscopy, scanning electron microscope, and atomic force microscope. The results indicated the composition of IZO thin films can be controlled by adjusting power supply to targets. The electrical properties of the Zn2In2O5 films were relatively independent of substrate temperatures between RT and 250. With low-temperature depositions using magnetron sputtering, the spatial resistivity distribution on the substrate surface for Zn2In2O5 films was smaller in comparison with those for ZnO and ITO films. The resistance of Zn2In2O5 film was more stable than ZnO or In2O3 films in oxidizing environments at high temperatures.
Time Period ThP Sessions | Topic C Sessions | Time Periods | Topics | ICMCTF2004 Schedule