Solid State Phenomena Vols. 124-126

Abstract: We have studied the Au+Ga alloy seeding method. Single-crystal GaN nano-column arrays were grown using metalorganic chemical vapor deposition (MOCVD) and their properties were investigated as a function of the growth parameters and Au thin film thickness. Au-coated Si(111) substrates were used for the growth of GaN nano-columns. The diameter and length of as-grown nano-column ranged from 100 to 500 nm and 1 to 5 μm, respectively. The morphology of the columns was investigated using scanning electron microscopy. Energy dispersive X-ray spectroscopy and photoluminescence were used for evaluating of its qualitative analysis and to evaluate the optical properties, respectively. Two important growth parameters were considered, the thickness of the Au thin film and the gallium flow rate. The density and tendency of the nano-columns depend on each of these growth parameters. It is believed that the catalytic activity of gold is determined by the size of the Au+Ga solid solution particles, and smaller Au+Ga clusters showed significant reactivity in the growth of one-dimensional GaN nano structures.

Abstract: Multi-component ZnO-In2O3-SnO2 thin films have been prepared by RF magnetron co-sputtering using targets composed of In4Sn3O12(99.99%) [1] and ZnO(99.99%) at room temperature. In4Sn3O12 contains less In than commercial ITO, so that it lowers cost. Working pressure was held at 3 mtorr flowing Ar gas 20 sccm and sputtering time was 30 min. RF power ratio [RF1 / ( RF1 + RF2 )] of two guns in sputtering system was varied from 0 to 1. Each RF power was varied 0~100W respectively. The thicknesses of the films were 350~650nm. The composition concentrations of the each film were measured with EPMA and AES. The low resistivity of 1-2 × 10-3 and an average transmittance above 80% in the visible range were attained for the films over a range of δ (0.3 ≤ δ ≤ 0.5). The films also showed a high chemical stability with time and a good uniformity.

Abstract: We have developed a large area, flat panel detector for general applications to digital radiology. This paper presents the x-ray detection characteristics with various semiconductor radiation detectors (HgI2, PbI2, PbO, CdTe) derived by a novel wet coating process for large area deposition. The wet coating process could easily be made from large area films with printing paste mixed with semiconductor and binder material at room temperature. X-ray performance data such as dark current, sensitivity and signal to noise ratio (SNR) were evaluated. The HgI2 semiconductor was shown in much lower dark current than the others, and also has the best sensitivity. In this paper, reactivity and combination characters of semiconductor and binder material that affect electrical and x-ray detection properties would be verified through our experimental results.

Abstract: We have grown delta-doped In0.5Ga0.5As /In0.5Al0.5As heterostructures on GaAs substrate applying with InxAl1-xAs compositional graded-step buffers, called metamorphic structures, grown by molecular beam epitaxy. Three types of buffer layers with different compositional gradients and thicknesses have designed to investigate the influence of the strain relaxation process. We characterized the samples by using transmission electron microscopy, triple-axis X-ray diffraction and Hall measurement. Two samples with different compositional gradient show almost same results in electrical properties. On the other hand, it is found that samples with different step thicknesses had shown the large differences in epilayer tilt and mosaic spread in the step-graded buffers. These results indicate that there exists an interrelation between the strain-relaxed buffer and 2DEG transport properties.

Abstract: Al-doped ZnO (ZnO:Al) films for transparent electrode applications in dye-sensitized solar cells and thin film solar cells were fabricated and characterized. In order to investigate the effect of crystallinity of the ZnO:Al films to the morphology and optical properties of the etched surface, the ZnO:Al films were deposited with varying substrate temperature by rf magnetron sputtering system and then films’ surface was etched in diluted hydrochloric acid (HCl) solution. Surface morphology of the amorphous ZnO:Al film deposited at room temperature was controllable to have large surface area, but it was not appropriate for transparent electrode layers due to high electrical resistivity. However, the resistivities of the ZnO:Al films deposited at the substrate temperatures of 150 and 300 oC were as low as 1.50×10-3
cm. In addition, the surface morphologies of the films deposited at 150 and 300 oC showed larger surface area for dye-sensitized cells and crater shape for light diffusion through the films, respectively. The surface morphologies and optical properties of the etched ZnO:Al films are attributed to the crystallinity of the as-fabricated films.

Abstract: In this study,
We
present ZnO thin films using electrochemical deposition method. ZnO thin films are deposited onto metal(Cu) and semiconductor (n-type Si) substrates. The electrolyte consists of a 0.1M Zn(NO3)2 solution, and we applied various potentials at different bath temperatures. XRD shows preferential orientation to (002) that increases with the applied cathodic potential and the bath temperature. Similar tendency is shown on both Cu and n-type Si substrates. SEM micrographs show ZnO surface morphology is greatly affected by the applied cathodic potentials. The RBS analysis reflects the rough morphology of ZnO thin film. The composition ratio Zn:O on n-type Si substrate is determined to be 1.0:1.3 ± 0.3 at the cathodic potential of -1.0[V] and the cell temperature of 70.

Abstract: Electron beam induced deposition (EBID) was carried out with gas introduction systems attached to field emission scanning electron microscope (FE-SEM). Using iron carbonyl and ferrocene, three dimensional (3-D) antenna structures were fabricated in the range of 30-50 nm in diameter and 500-1000 nm in size. Post-deposition annealing of iron nanostructures resulted in the formation of crystalline alpha-iron and iron carbide phases. The iron concentration was controlled by the partial pressure of iron carbonyl and ferrocene. Electron holography observation with field emission transmission electron microscopy (FE-TEM) revealed that the remanent magnetic flux density Br of the nanostructures also depends on the iron concentration.

Abstract: We report important factors affecting the dielectric properties of CaCu3Ti4O12 (CCTO) polycrystalline ceramics prepared by the conventional solid-state ceramic process. The relative dielectric constants (εr) up to several thousands (~ 3,000 at 1 kHz) were gradually increased with increasing the sintered density of samples in the case that no exaggerated grain growth occurred. An abrupt increase in εr values were, however, accompanied by the formation of abnormally grown large grains, and thus with increasing the population of abnormally grown grains, which could be achieved by a prolonged sintering at 1060°C, the εr values were remarkably increased from several thousands to ~105. Optimally processed CCTO sample exhibited a very high εr of ~ 90,000 at 1 kHz.

Abstract: Embossing lithography is one of the most promising technologies for mass production of nano-scale structures. To advance the industrialization of embossing lithography, fabrication of low cost, high mechanical strength embossing template is essential. Electroformed Ni template can be used as an embossing template if its poor anti-adhesive property is fixed by proper releasing layer treatment, especially, when it is used with sticky thermoset polymer. In this experiment, quartz master template with 200nm to 2um sized surface protrusions was fabricated and used to emboss the PMMA coated Si wafer. Then the embossed PMMA layer was coated with metal seed layer (Ni) and electroplating of Ni was followed to fabricate Ni template. To apply anti-stiction SAM layer, SiO2 and Si layer was coated on Ni template. With proper anti-stiction treatment of Ni template, sub-micron patterns were successfully transferred to sticky thermoset polymers such as epoxy resin using Ni template without any degradation of anti-adhesive property.

Abstract: Pb(Zr, Ti)O3 thin films were successfully prepared on (111)Pt/IrO2/SiO2/(100)Si substrates using SrTiO3 seeds at 290 oC by RF inductive heating type and 350 oC by resistive heating type metalorganic chemical vapor deposition method (MOCVD), respectively. The SrTiO3 was chosen as seed layers and prepared by pulsed laser deposition method. The crystal structures and orientations of SrTiO3 seeds were changed by deposition temperature. In the case of preparation with RF inductive heating MOCVD, the remanent polarization (2Pr) and coercive field (2Ec) were 42 μC/cm2 and 256 kV/cm, respectively.