Browsing by Author "Li, Zhi-Qing"

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Decoding CMOS Rolling-Shutter Pattern in Translational or Rotational Motions for VLC
(2019-04-01)
Chow, Chi-Wai
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Li, Zhi-Qing
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Chuang, Yu-Cheng
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Liao, Xin-Lan
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Lin, Kun-Hsien
We propose and demonstrate a CMOS rolling-shutter pattern decoding scheme based on two newly introduced schemes, named row grayscale redistribution and differential grayscale packet selection to improve the performance in decoding the CMOS rolling-shutter pattern in translational or rotational motions. Results show that even the CMOS image sensor is in translational or rotational motions, no significant signal degradation is observed at wireless transmission distance up to 150 cm. The maximum visible light communication data rate at different wireless transmission distances is also analyzed.
Electrical conduction processes in ZnO in a wide temperature range 20-500 K
(2011-09-15)
Lien, Chien-Chi
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Wu, Chih-Yuan
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Li, Zhi-Qing
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Lin, Juhn-Jong
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電子物理學系
We have investigated the electrical conduction processes in as-grown and thermally cycled ZnO single crystal as well as as-grown ZnO polycrystalline films over the wide temperature range 20-500 K. In the case of ZnO single crystal between 110 and 500 K, two types of thermal activation conduction processes are observed. This is explained in terms of the existence of both shallow donors and intermediately deep donors that are consecutively excited to the conduction band as the temperature increases. By measuring the resistivity rho(T) of a given single crystal after repeated thermal cycling in vacuum, we demonstrate that oxygen vacancies play an important role in governing the shallow donor concentrations but leave the activation energy (similar or equal to 27 +/- 2 meV) largely intact. In the case of polycrystalline films, two types of thermal activation conduction processes are also observed between similar to 150 and 500 K. Below similar to 150 K, we found an additional conductionprocess due to the nearest-neighbor-hopping conduction mechanism, which takes place in the shallow impurity band. As the temperature further decreases below similar to 80 K, a crossover to the Mott variable-range-hopping conduction process is observed. Taken together with our previous measurements on rho(T) of ZnO polycrystalline films in the temperature range 2-100 K [Y. L. Huang et al., J. Appl. Phys. 107, 063715 (2010)], this work establishes a quite complete picture of the overall electrical conduction mechanisms in the ZnO material from liquid-helium temperatures up to 500 K. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3638120]
Electron dephasing in homogeneous and inhomogeneous indium tin oxide thin films
(2012-03-05)
Wu, Chih-Yuan
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Lin, Bo-Tsung
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Zhang, Yu-Jie
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Li, Zhi-Qing
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Lin, Juhn-Jong
The electron dephasing processes in two-dimensional homogeneous and inhomogeneous indium tin oxide thin films have been investigated in a wide temperature range 0.3-90 K. We found that the small-energy-transfer electron-electron (e-e) scattering process dominated the dephasing from a few kelvins to several tens of kelvins. At higher temperatures, a crossover to the large-energy-transfer e-e scattering process was observed. Below about 1 to 2 K, the dephasing time tau(phi) revealed a very weak temperature dependence, which intriguingly scaled approximately with the inverse of the electron diffusion constant D, i.e., tau(phi)(T approximate to 0.3 K) proportional to 1/D. Theoretical implications of our results are discussed. The reason why the electron-phonon relaxation rate is negligibly weak in this low-carrier-concentration material is presented.
Electron-electron interaction effect on longitudinal and Hall transport in thin and thick Ag-x(SnO2)(1-x) granular metals
(2015-03-03)
Wu, Ya-Nan
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Wei, Yan-Fang
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Li, Zhi-Qing
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Lin, Juhn-Jong
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電子物理學系
We study the temperature behaviors of the Hall coefficient, R-H, and longitudinal conductivity, sigma, of two series of Ag-x(SnO2)(1-x) (x being the Ag volume fraction) granular films lying in the metallic regime. The first (second) series of films are similar to 500 (similar to 9) nm thick and constitute a three-(two-) dimensional granular array. In the high-x regime with g(T) >> g(T)(c) (g(T) being the dimensionless intergrain tunneling conductance, and g(T)(c) being the critical tunneling conductance at the percolation threshold), we observe a R-H alpha ln T law from similar to 6 to 300K. This ln T behavior is independent of array dimensionality. We also observe a sigma alpha ln T law in the temperature range similar to 20-100 K. Below similar to 10 K, the temperature behavior of sigma changes to a root T dependence in thick films, while it changes to a different ln T dependence in thin films. The overall R-H and sigma characteristics can be explained by the electron-electron interaction (EEI) effects in the presence of granularity. As x is reduced and approaches the percolation threshold, we found that the ln T dependences of R-H and sigma still hold for a wide temperature range. We propose an explanation for the long-standing puzzle of the sigma alpha ln T dependence, which has previously been frequently observed in composite systems near the quantum percolation threshold, as arising from the same EEI effect considered in the recent theory of granular metals.
Electronic conduction properties of indium tin oxide: single-particle and many-body transport
(2014-08-27)
Lin, Juhn-Jong
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Li, Zhi-Qing
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電子物理學系
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Department of Electrophysics
Indium tin oxide (Sn-doped In2O3-delta or ITO) is a very interesting and technologically important transparent conducting oxide. This class of material has been extensively investigated for decades, with research efforts mostly focusing on the application aspects. The fundamental issues of the electronic conduction properties of ITO from room temperature down to liquid-helium temperatures have rarely been addressed thus far. Studies of the electrical-transport properties over a wide range of temperature are essential to unravelling the underlying electronic dynamics and microscopic electronic parameters. In this topical review, we show that one can learn rich physics in ITO material, including the semi-classical Boltzmann transport, the quantum-interference electron transport, as well as the many-body Coulomb electron-electron interaction effects in the presence of disorder and inhomogeneity (granularity). To fully reveal the numerous avenues and unique opportunities that the ITO material has provided for fundamental condensed matter physics research, we demonstrate a variety of charge transport properties in different forms of ITO structures, including homogeneous polycrystalline thin and thick films, homogeneous single-crystalline nanowires and inhomogeneous ultrathin films. In this manner, we not only address new physics phenomena that can arise in ITO but also illustrate the versatility of the stable ITO material forms for potential technological applications. We emphasize that, microscopically, the novel and rich electronic conduction properties of ITO originate from the inherited robust free-electron-like energy bandstructure and low-carrier concentration (as compared with that in typical metals) characteristics of this class of material. Furthermore, a low carrier concentration leads to slow electron-phonon relaxation, which in turn causes the experimentally observed (i) a small residual resistance ratio, (ii) a linear electron diffusion thermoelectric power in a wide temperature range 1-300 K and (iii) a weak electron dephasing rate. We focus our discussion on the metallic-like ITO material.
Giant Hall effect in nonmagnetic Mo/SnO(2) granular films
(2010-09-17)
Wu, Ya-Nan
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Li, Zhi-Qing
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Lin, Juhn-Jong
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電子物理學系
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物理研究所
We have measured the resistivities and Hall coefficients, R(H), of a series of nonmagnetic Mo(x)(SnO(2))(1-x) nanogranular films with the Mo volume fraction x ranging from similar to 0.29 to 1. We found that the magnitude of R(H)(2 K) largely increased by a factor of similar to 800 as x was reduced from similar to 0.8 to similar or equal to 0.36. Then, it slightly decreased with a further decrease in x down to similar or equal to 0.32, which was determined to be the classical percolation threshold, x(c), from the resistivity dependence on x. This nearly 3 orders of magnitude enhancement in R(H) at a metal volume fraction x > x(c) is explained in terms of the recent theoretical concept of the local quantum-interference effect induced giant Hall effect in granular systems.
Giant Hall effect in nonmagnetic Mo/SnO2 granular films
(2010-09-17)
Wu, Ya-Nan
;
Li, Zhi-Qing
;
Lin, Juhn-Jong
;
電子物理學系
;
物理研究所
We have measured the resistivities and Hall coefficients, R-H, of a series of nonmagnetic Mo-x(SnO2)(1-x) nanogranular films with the Mo volume fraction x ranging from similar to 0.29 to 1. We found that the magnitude of R-H(2 K) largely increased by a factor of similar to 800 as x was reduced from similar to 0.8 to similar or equal to 0.36. Then, it slightly decreased with a further decrease in x down to similar or equal to 0.32, which was determined to be the classical percolation threshold, x(c), from the resistivity dependence on x. This nearly 3 orders of magnitude enhancement in R-H at a metal volume fraction x > x(c) is explained in terms of the recent theoretical concept of the local quantum-interference effect induced giant Hall effect in granular systems.
Logarithmic temperature dependence of Hall transport in granular metals
(2011-08-12)
Zhang, Yu-Jie
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Li, Zhi-Qing
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Lin, Juhn-Jong
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電子物理學系
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物理研究所
We have measured the Hall coefficient R-H and the electrical conductivity sigma of a series of ultrathin indium-tin-oxide films between 2 and 300 K. A robust R-H proportional to ln T law is observed in a considerably wide temperature range of 2 and similar to 120 K. This ln T dependence is explained as originating from the electron-electron interaction effect in the presence of granularity as theoretically predicted. Furthermore, we observed sigma proportional to ln T law from 3 K up to several tens K, which also arose from the Coulomb interaction effect in inhomogeneous systems. These results provide strong experimental support for the current theoretical concepts for charge transport in granular metals with intergrain tunneling conductivity g(T) >> 1.
Variable-range-hopping conduction processes in oxygen deficient polycrystalline ZnO films
(2010-03-15)
Huang, Yung-Lung
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Chiu, Shao-Pin
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Zhu, Zhi-Xin
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Li, Zhi-Qing
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Lin, Juhn-Jong
We have fabricated oxygen deficient polycrystalline ZnO films by the rf sputtering deposition method. To systematically investigate the charge transport mechanisms in these samples, the electrical resistivities have been measured over a wide range of temperature from 300 K down to liquid-helium temperatures. We found that below about 100 K, the variable-range-hopping (VRH) conduction processes govern the charge transport properties. In particular, the Mott VRH conduction process dominates at higher temperatures, while crossing over to the Efros-Shklovskii (ES) VRH conduction process at lower temperatures. The crossover occurred at temperatures as high as a few tens degrees kelvin. Moreover, the temperature behavior of resistivity over the entire VRH conduction regime from the Mott-type to the ES-type process can be well described by a universal scaling law.
Visible light communication and positioning using positioning cells and machine learning algorithms
(2019-05-27)
Chuang, Yu-Cheng
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Li, Zhi-Qing
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Hsu, Chin-Wei
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Liu, Yang
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Chow, Chi-Wai
We propose and experimentally demonstrate a practical visible light position (VLP) system using repeated unit cells and machine learning (ML) algorithms. ML is employed to increase the positioning accuracy. Algorithms of the 2nd-order regression ML model and the polynomial trilateral ML model are discussed. More than 80% of the measurement data have position error within 4 cm when using the 2nd-order regression ML model, while the position error is within 5 cm when using the polynomial trilateral ML model. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement