Browsing by Author "Chiu, C. W."

Now showing 1 - 3 of 3

Coulomb scattering rates of excited carriers in moderate-gap carbon nanotubes
(2006-06-01)
Chiu, C. W.
;
Shyu, F. L.
;
Chang, C. P.
;
Chuu, D. S.
;
Lin, M. F.
Temperature induces some free carriers in moderate-gap carbon nanotubes, which, thus, creates the low-frequency intraband e-h excitations. Such excitations are the effective deexcitation channels for the excited electrons (holes) in conduction (valence) bands, while they are very weak. The Coulomb decay rates of the lowest two conduction bands are sensitive to the changes in wave vector, radius, and temperature. However, those of the band-edge states depend on chirality weakly. These results directly reflect the strong energy dispersions and the temperature-dependent electron distributions. The calculated results are roughly consistent with the experimental measurements from the ultrafast optical spectroscopies.
DC dynamic pull-in predictions for a generalized clamped-clamped micro-beam based on a continuous model and bifurcation analysis
(2008-11-01)
Chao, Paul C-P
;
Chiu, C. W.
;
Liu, Tsu-Hsien
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This study is devoted to providing precise predictions of the dc dynamic pull-in voltages of a clamped-clamped micro-beam based on a continuous model. A pull-in phenomenon occurs when the electrostatic force on the micro-beam exceeds the elastic restoring force exerted by beam deformation, leading to contact between the actuated beam and bottom electrode. DC dynamic pull-in means that an instantaneous application of the voltage ( a step function such as voltage) is applied. To derive the pull-in voltage, a dynamic model in partial differential equations is established based on the equilibrium among beam flexibility, inertia, residual stress, squeeze film, distributed electrostatic forces and its electrical field fringing effects. The method of Galerkin decomposition is then employed to convert the established system equations into reduced discrete modal equations. Considering lower-order modes and approximating the beam deflection by a different order series, bifurcation based on phase portraits is conducted to derive static and dynamic pull-in voltages. It is found that the static pull-in phenomenon follows dynamic instabilities, and the dc dynamic pull-in voltage is around 91-92% of the static counterpart. However, the derived dynamic pull-in voltage is found to be dependent on the varied beam parameters, different from a fixed predicted value derived in past works, where only lumped models are assumed. Furthermore, accurate closed-form predictions are provided for non-narrow beams. The predictions are finally validated by finite element analysis and available experimental data.
High-performance GaN-based vertical-injection light-emitting diodes with TiO2-SiO2 omnidirectional reflector and n-GaN roughness
(2007-03-01)
Huang, H. W.
;
Kuo, H. C.
;
Lai, C. F.
;
Lee, C. E.
;
Chiu, C. W.
We have designed and fabricated a new type of GaN-based thin-film vertical-injection light-emitting diode (LED) with TiO2-SiO2 onmidirectional reflector (ODR) and n-GaN roughness. The associated ODR designed for LED operation wavelength at 455 nm vias integrated with patterned conducting channels for the purpose of vertical current spreading. With the help of laser lift-off and. photo-electrochemical etching technologies, at a driving current of 350 mA and with chip size of 1 mm x 1 mm, the light-output power and the external quantum efficiency of our thin-film LED with TiO2-SiO2 ODR reached 330 mW and 26.7%. The result demonstrated 18% power enhancement when compared with the results from the thin-film LED with Al reflector replace.