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Aluminum-Doped Zinc Oxide Thin Films Prepared by Sol-Gel and~RF Magnetron Sputtering

100%
Wu G., Chen Y., Lu H.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 1
149-152
EN
Zinc oxide (ZnO) thin films have become technologically important materials due to their wide range of electrical and optical properties. The characteristics can be further adjusted by adequate doping processes. In this paper, aluminum-doped zinc oxide thin films have been prepared on glass substrates using a sol-gel route and the radio-frequency magnetron sputtering process. The stoichiometry could be easily adjusted by controlling the nanosized precursor concentration and the thickness by dip-coating cycles. On the other hand, the mixed N_2O/Ar plasma gas provided adequate N doping for the RF sputtering process. The results showed the low electrical resistivity of 21.5 Ω cm with the carrier concentration of - 3.21 × 10^{18} cm^{-3} for the n-type aluminium-doped zinc oxide film. They were 34.2 Ω cm and + 9.68 × 10^{16} cm^{-3} for the p-type aluminium-doped zinc oxide film. The optical transmittance has been as high as 85-90% in the 400-900 nm wavelength range. The aluminium-doped zinc oxide (2 at.% Al) films exhibited the hexagonal wurzite structure with (002) preferred crystal orientation. The electrical characteristics were depicted by the gradual increase in N and NO that occupy the oxygen vacancies.
2
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Improved Light Extraction Efficiency by Photonic Crystal Arrays on Transparent Contact Layer Using Focused Ion Beams

100%
Wu G., Tsai B., Kung S., Wu C.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 1
140-143
EN
Nitride-based thin-film materials have become increasingly important for the high brightness light-emitting diode applications. The improvements in light extraction and lower power consumption are highly desired. Although the internal quantum efficiency of GaN-based LED has been relatively high, only a small fraction of light can be extracted. In this study, a new design of two-dimensional photonic crystal array has been prepared on the top transparent contact layer of indium-tin oxide film to improve the light extraction efficiency using focused ion beam. The acceleration voltage of the Ga dual-beam nanotechnology system SMI 3050 was 30 kV and the ion beam current was 100 pA. The cylindrical air holes had the diameter of 150 nm and depth of 100 nm. The micro photoluminescence analysis results showed that the light output intensity could be 1.5 times of that of the non-patterned control sample. In addition, the structural damage from the focused ion beam drilling of GaN step could be eliminated. The excellent I-V characteristics have been maintained, and the external light extraction efficiency would be still improved for the LED devices.
3
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Ion Beam Surface Modification of GaN Films for High Efficient Light Emitting Diodes

100%
Wu G., Lin Y., Tu K.
Acta Physica Polonica A
|
2013
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vol. 123
|
issue 5
884-887
EN
Focused gallium (Ga) ion beam technology has been proposed to modify the surface of GaN thin films. Due to the significant advancement in nitride semiconductors, the solid-state light emitting diodes will gradually replace fluorescent lamps in the next decade. However, further improvements in light extraction and power efficiency are still highly desired. GaN is limited by its high refractive index, with low light escape cone angle at about 24.6°. The external quantum efficiency is low due to the unwanted reflection and absorption. As the patterning technology scales down to the nanometer level, photonic crystal lattice in the visible light wavelength range can be achieved. Therefore, we improved the external efficiency by the new design of hexagonal photonic crystal lattice with air hole arrays in the diameter of 150 nm and the depth of 120 nm. The Ga beam was accelerated at 30 kV and the ion current was 100 pA. The plane wave expansion method along with the finite difference time domain was useful to investigate the quantum confinement. The nanopatterning by the focused ion beam could save time and processing step. In addition, we have successfully prepared blue InGaN/GaN samples with hexagonal period of 200 nm. The device micro-photoluminescence results have demonstrated that the peak illumination intensity was improved by 30%.
4
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Improved Nucleation and Transition by Plasma Treatments for Fast Response Optically-Compensated-Bend Displays

100%
Wu G., Huang C., Chien H.
Acta Physica Polonica A
|
2013
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vol. 123
|
issue 5
892-895
EN
The optically-compensated-bend mode pi-cell displays exhibit fast-response time and wide-viewing angle characteristics. However, it requires a transition of the liquid crystal molecule from an initial splay state to the bend state configuration before providing the quick operation. A high voltage and a long warm-up time are needed to transform to the bend state. In this paper, the polyimide alignment films have been modified to reduce the splay-to-bend transition time by plasma beam treatments. The proposed method was demonstrated to be highly effective in improving the overall transition time. The number of splay-to-bend nucleation sites in the assembled liquid crystal cells could be increased dramatically by up to 20 times at the initial stage, and the improvement in the cell warm-up time was achieved at 45-71% reduction at 5.5 V. The plasma processing parameters were optimized at the plasma power of 700 W, the plasma distance of 25 mm, and the plasma scan speed of 600 mm/s. In addition, we maintained the excellent optical properties and response time characteristics for the optically-compensated-bend mode liquid crystal displays.
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