T. P. Chen

Nanyang Technological University, Tumasik, Singapore

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Publications (200)415.21 Total impact

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    Dataset: scholar (1)
  • X. D. Li, T. P. Chen, Y. Liu, K. C. Leong
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    ABSTRACT: Evolution of dielectric function of Al-doped ZnO (AZO) thin films with annealing temperature is observed. It is shown that the evolution is due to the changes in both the band gap and the free-electron absorption as a result of the change of free-electron concentration of the AZO thin films. The change of the electron concentration could be attributed to the activation of Al dopant and the creation/annihilation of the donor-like defects like oxygen vacancy in the thin films caused by annealing.
    Optics Express 09/2014; 22(19). · 3.55 Impact Factor
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    Nanoscience and Nanotechnology Letters. 09/2014; 6(9):729-757.
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  • X D Li, T P Chen, Y Liu, K C Leong
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    ABSTRACT: The contributions of localized surface plasmon resonance (LSPR) and Drude (free electrons) absorption to the complex dielectric function of ultrathin Au films were investigated with spectroscopic ellipsometry. When the Au film thickness is thinner than ~10 nm, Au nanoparticles (NPs) are formed as a result of the discontinuity in the films, leading to the emergence of LSPR of Au NPs; and the LSPR exhibits a splitting when the films thinner than ~8 nm, which could be attributed to the near-field coupling of the Au NPs and/or the inhomogeneous polarizations of the Au NPs. On the other hand, the delocalization of electrons in Au NPs due to the aggregation of Au NPs in a thicker film leads to an increase in the free-electron absorption and a suppression of the LSPR.
    Optics Express 03/2014; 22(5):5124-32. · 3.55 Impact Factor
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    ABSTRACT: A write-once-read-many-times (WORM) memory devices based on O2 plasma-treated indium gallium zinc oxide (IGZO) thin films has been demonstrated. The device has a simple Al/IGZO/Al structure. The device has a normally OFF state with a very high resistance (e.g., the resistance at 2 V is ∼109 Ω for a device with the radius of 50 μm) as a result of the O2 plasma treatment on the IGZO thin films. The device could be switched to an ON state with a low resistance (e.g., the resistance at 2 V is ∼103 Ω for the radius of 50 μm) by applying a voltage pulse (e.g., 10 V/1 μs). The WORM device has good data-retention and reading-endurance capabilities.
    Applied Physics Letters 01/2014; 104(3):033505-033505-4. · 3.52 Impact Factor
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    ABSTRACT: Dielectric function, band gap, and exciton binding energies of ultrathin ZnO films as a function of film thickness have been obtained with spectroscopic ellipsometry. As the film thickness decreases, both real (ε1) and imaginary (ε2) parts of the dielectric function decrease significantly, and ε2 shows a blue shift. The film thickness dependence of the dielectric function is shown related to the changes in the interband absorption, discrete-exciton absorption, and continuum-exciton absorption, which can be attributed to the quantum confinement effect on both the band gap and exciton binding energies.
    Journal of Applied Physics 01/2014; 115(10):103512-103512-5. · 2.21 Impact Factor
  • Thin Solid Films 10/2013; · 1.87 Impact Factor
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    S G Hu, Y Liu, T P Chen, Z Liu, Q Yu
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    ABSTRACT: The well-known Ebbinghaus forgetting curve, which describes how information is forgotten over time, can be emulated using a NiO-based memristor with conductance that decreases with time after the application of electrical pulses. Here, the conductance is analogous to the memory state, while each electrical pulse represents a memory stimulation or learning event. The decrease in the conductance with time depends on the stimulation parameters, including pulse height and width and the number of pulses, which emulates memory loss behavior well in that the time taken for the memory to be lost depends on how the information is learned.
    Applied Physics Letters 09/2013; 103(133701). · 3.52 Impact Factor
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    ABSTRACT: A triple-layer anti-reflection coating (TL-ARC) with Si nanocrystals (nc-Si)-dielectric nanocomposite thin film structure is proposed for Si solar cells. The TL-ARC has a graded refractive index (RI) profile of high RI, medium RI, and low RI. Such RI profile is achieved with the structure consisting of a Si3N4 layer embedded with high concentration of nc-Si and another Si3N4 layer embedded with low concentration of nc-Si and a SiO2 layer. The design of the TL-ARC is carried out with the calculation of the effective indices of the high-RI and medium-RI layers with the Maxwell-Garnett effective medium approximation model. Due to the photoluminescence properties of nc-Si embedded in Si3N4 matrix, the TL-ARC has the inherent capability of down-converting ultraviolet photons to low-energy photons that are useful to Si solar cells. The deposition of the TL-ARC on Si solar cell is fabricated with plasma enhanced chemical vapor deposition in a single process step. The performance enhancement of Si solar cells by the TL-ARC has been demonstrated by experiments.
    Journal of Applied Physics 08/2013; 114(5). · 2.21 Impact Factor
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    X D Li, T P Chen, P Liu, Y Liu, K C Leong
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    ABSTRACT: Band gaps and exciton binding energies of undoped and Al-doped ZnO thin films were determined from optical absorption measurement based on the Elliott's exciton absorption theory. As compared to the undoped films, the doped films exhibit a band gap expansion and a reduction in the exciton binding energies due to the free electron screening effect, which suppresses the excitonic absorption and results in a blue shift of the absorption edge. The undoped and doped films show the same quantum size dependence, i.e. both the exciton binding energies and band gap energies increase with decreasing grain size of the oxides.
    Optics Express 06/2013; 21(12):14131-14138. · 3.55 Impact Factor
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    ABSTRACT: We study the paired-pulse-induced response of a NiOx-based memristor. The behavior of the memristor is surprisingly similar to the paired-pulse facilitation of a biological synapse. When the memristor is stimulated with a pair of electrical pulses, the current of the memristor induced by the second pulse is larger than that by the first pulse. In addition, the magnitude of the facilitation decreases with the pulse interval, while it increases with the pulse magnitude or pulse width.
    Applied Physics Letters 05/2013; 102(18). · 3.52 Impact Factor
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    ABSTRACT: This paper presents a design of electronic synapse with Spike Time Dependent Plasticity (STDP) based on resistive memory device. With the resistive memory device whose resistance can be purposely changed, the weight of the synaptic connection between two neurons can be modified. The synapse can work according to the STDP rule, ensuring that the timing between pre and post-spikes leads to either the long term potentiation or long term depression. By using the synapse, a neural network with three neurons has been constructed to realize the STDP learning.
    Journal of Applied Physics 03/2013; 113(11). · 2.21 Impact Factor
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    ABSTRACT: The effect of short-duration ultraviolet (UV) exposure on the threshold voltage (Vth) of amorphous indium gallium zinc oxide thin film transistors (TFTs) and its recovery characteristics were investigated. The Vth exhibited a significant negative shift after UV exposure. The Vth instability caused by UV illumination is attributed to the positive charge trapping in the dielectric layer and/or at the channel/dielectric interface. The illuminated devices showed a slow recovery in threshold voltage without external bias. However, an instant recovery can be achieved by the application of positive gate pulses, which is due to the elimination of the positive trapped charges as a result of the presence of a large amount of field-induced electrons in the interface region.
    Applied Physics Letters 01/2013; 103(20):202110-202110-4. · 3.52 Impact Factor
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    ABSTRACT: A nonvolatile memory based on ink-jet printed In-Ga-Zn oxide (IGZO) thin film transistor with bottom gate bottom contact architecture is reported. The memory device contains SiO2 gate dielectric layer embedded with silicon nanocrystals, which act as charge trapping sites. Memory effects were observed by a clockwise loop in Vgs-Id curves, which is attributed to the charging and discharging of the silicon nanocrystals. The printed IGZO memory exhibits a high (about 1 × 103) on/off ratio.
    Nanoelectronics Conference (INEC), 2013 IEEE 5th International; 01/2013
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    ABSTRACT: Effective control of room-temperature electroluminescence of n-ZnMgO/p-GaN light-emitting diodes (LEDs) over both emission intensity and wavelength is demonstrated. With varied Mg concentration, the intensity of LEDs in the near-ultraviolet region is increased due to the effective radiative recombination in the ZnMgO layer. Furthermore, the emission wavelength is shifted to the green/yellow spectral region by employing an indium-tin-oxide thin film as the dopant source, where thermally activated indium diffusion creates extra deep defect levels for carrier recombination. These results clearly demonstrate the effectiveness of controlled metal incorporation in achieving high energy efficiency and spectral tunability of the n-ZnMgO/p-GaN LED devices.
    Applied Physics Letters 12/2012; 101(26). · 3.52 Impact Factor
  • W. Zhu, T. P. Chen, Y. Liu, S. Fung
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    ABSTRACT: In this work, conduction mechanisms of Al/anodic Al oxide/ Al structure, which exhibits resistive switching behavior, have been investigated. The low-resistance state shows ohmic conduction with a metal-like behavior similar to that of pure aluminum. The situation can be explained by the existence of the metallic filament formed by the excess Al in the Al oxide. On the other hand, the high-resistance state (HRS) shows two distinct regimes: ohmic conduction at low fields with a semiconductor-like behavior; and a non-ohmic conduction at high fields. The ohmic conduction of HRS at low fields is attributed to the electron hopping between the states in the oxide with the activation energy of ∼0.23 eV. It is suggested that the conduction of HRS at high fields (the maximum voltage is lower than the set voltage) is due to the field-enhanced thermal excitation of the electrons trapped in the states of the metallic Al nano-phase into the conduction band of the Al oxide or the electron emission from the potential well of the metallic Al nano-phase to the conduction band.
    Journal of Applied Physics 09/2012; 112(6). · 2.21 Impact Factor
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    ABSTRACT: Resistive switching behavior of partially anodized aluminum thin film has been investigated at temperatures of 25 $^{circ}hbox{C}$–250 $^{circ}hbox{C}$. Both the reset and set voltages decrease with increasing temperature, showing Arrhenius-like dependence with small activation energies. The pulse voltage experiment also suggests that the conductive filament breaking/reconnection is easier to occur at a higher temperature. Some possible mechanisms for the phenomena are discussed. On the other hand, at elevated temperatures without continuous electric field applied, while the high-resistance state exhibits no significant change with time, the low-resistance state (LRS) shows a continuous degradation, and there is a sudden failure. The LRS failure time shows Arrhenius dependence with an activation energy of $sim$1.3 eV, suggesting that the LRS failure could be due to the migration of the excess Al atoms at high temperatures.
    IEEE Transactions on Electron Devices 09/2012; 59(9):2363-2367. · 2.06 Impact Factor
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    Q Yu, W M Lim, S G Hu, T P Chen, L J Deng, Y Liu
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    ABSTRACT: In this work, a flexible memory device based on resistive switching in a NiO thin film has been demonstrated. A large memory window with the resistance ratio of ∼ 10 3 between the high-resistance state and the low-resistance state is observed. A memory state can be altered by either voltage pulses or a voltage sweeping. The memory window can be maintained in repetitive programming/erase cycles (at least 120 cycles have been demonstrated in the present experiment), showing a good endurance. In addition, in the time frame (10 4 s) of the retention experiment, no sig-nificant degradation in the memory window is observed, demonstrating a good retention capability.
    Nanoscience and Nanotechnology Letters 08/2012; · 1.44 Impact Factor
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    ABSTRACT: Using a two-step fabrication technique (pulsed laser deposition (PLD) and H2 surface treatment), we fabricated ZnO thin films that could emit ultra-strong green emission with coexistence of random lasing phenomenon. After PLD deposition, the as-prepared undoped ZnO thin films (200–500 nm) were annealed in Ar 95%–H25% ambient at 500 °C. The H2 treatment led to the formation of a porous structure that creates substantial optical cavities (diameter ∼1.3 µm). Surprisingly, these optical cavities tremendously amplified the green emission rather than ultraviolet (UV) emission. There was insignificant change in emission intensity after high-temperature annealing (700 °C) in O2 and acetone dipping, indicating the samples are thermally and chemically stable. The samples exhibited a high quantum yield of 32%. We studied the origin of this ultra-strong green emission using low-temperature photoluminescence, extensive structural study and cyclic annealing. The results suggested that neither hydrogen nor VO plays a role in green emission. The green emission was attributed mainly to the complex defects and the presence of structural defects in the porous structure. In addition, we demonstrated the feasibility of large-scale green emission ZnO fabrication via micro-size patterning, paving a way to practical optoelectronic applications.
    Journal of Physics D Applied Physics 05/2012; 45(18). · 2.53 Impact Factor

Publication Stats

1k Citations
415.21 Total Impact Points

Institutions

  • 2002–2014
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Tumasik, Singapore
  • 2011
    • Singapore University of Technology and Design
      • Division of Engineering Product Development
      Singapore
    • Institute of Microelectronics
      Tumasik, Singapore
  • 2009
    • Northeast Institute of Geography and Agroecology
      • Key Laboratory of Materials Physics
      Peping, Beijing, China
  • 2008
    • University of Electronic Science and Technology of China
      • State Key Laboratory of Electronic Thin Films and Integrated Devices
      Chengdu, Sichuan Sheng, China
    • Arizona State University
      • Department of Mechanical Engineering
      Tempe, AZ, United States
  • 2006
    • Nanjing University of Aeronautics & Astronautics
      Nan-ching, Jiangsu Sheng, China
  • 1993–2006
    • The University of Hong Kong
      • Department of Physics
      Hong Kong, Hong Kong
  • 2002–2004
    • Nanyang Normal University
      Nan-yang-shih, Henan Sheng, China