Browsing by Author "Wang, Yi-Chao"

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Characterization and Comparison of GaAs/AlGaAs Uni-Traveling Carrier and Separated-Transport-Recombination Photodiode Based High-Power Sub-THz Photonic Transmitters
(2010-01-01)
Li, Yu-Tai
;
Shi, Jin-Wei
;
Huang, C. -Y.
;
Chen, Nan-Wei
;
Chen, Shu-Han
We describe in detail the characterization of two high-power photonic transmitters based on two different kinds of high-power photodiodes, one a GaAs/AlGaAs based uni-traveling-carrier photodiode (UTC-PD) and the other a separated-transport-recombination photodiode (STR-PD). The diodes operate under optical pulse excitation at the 800 nm wavelength. Both PDs have the same total depletion layer thickness (same theoretical RC-limited bandwidth) and are m integrated with the same broadband micro-machined circular disk monopole antennas to radiate strong sub-THz pulses. However the STR-PD based transmitter exhibits very different dynamic and static performance from that of the UTC-PD based transmitter due to the existence of a low-temperature-grown GaAs (LTG-GaAs) based recombination center inside the active region, and the much thinner thickness of effective depletion layer. Under optical pulse excitation (similar to 480 pJ/pulse), the STR-PD based transmitter exhibits a much lower maximum averaged output photocurrent (1.2 mA versus 0.3 mA) than that of the UTC-PD transmitter, although the radiated electrical pulse-width and maximum peak-power, which are measured by the same THz time-domain spectroscopic (TDS) system, of both devices are comparable. These results indicate that although the recombination center in the STR-PD degrades its DC responsivity, it effectively improves the high-speed and output power performance of the device and eliminates the DC component of the photocurrent, which should minimize device-heating problem during high-power operation. The radiated waveforms of both devices under intense optical pulse illumination also exhibit excellent linearity and strong bias dependent magnitude. This suggests their suitability for application as photonic emitters and possibly as a data modulator in sub-THz impulse-radio communication systems.
Near-infrared femtosecond laser crystallized poly-Si thin film transistors
(2007-05-28)
Wang, Yi-Chao
;
Shieh, Jia-Min
;
Zan, Hsiao-Wen
;
Pan, Ci-Ling
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光電工程學系
Polycrystalline silicon (poly-Si) thin film transistors (TFTs) fabricated by near-infrared femtosecond laser annealing (FLA) are demonstrated. The FLA-annealed poly-Si channels exhibit low tail-state, deep-state, and midgap-state densities of grain traps. Characteristics such as field-effect mobility, threshold voltage, and subthreshold slope for FLA-annealed poly-TFTs are comparable to those of conventional approaches. A wide process window for annealing laser fluences was confirmed by examining the changes in electrical parameters for transistors with various channel dimensions. (C) 2006 Optical Society of America.
Nonvolatile memory with switching interfacial polar structures of nano Si-in-mesoporous silica
(2009-10-05)
Shieh, Jia-Min
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Huang, Jung Y.
;
Yu, Wen-Chien
;
Huang, Jian-Da
;
Wang, Yi-Chao
We show an artificially engineered electret with Si nanocrystals embedded in mesoporous silica for nonvolatile memory. We attribute the polarization to from polar layers lying at the interfaces between one-side bonded Si nanocrystals and mesoporous silica matrix. Under external field, the Si nanocrystals could be displaced in the porechannels causing displaced charge distributions and therefore a field-controllable electric polarization. Nonvolatile memory is demonstrated with a metal-oxide-semiconductor field-effect transistor. (C) 2009 American Institute of Physics. [doi:10.1063/1.3240888]
Optical sum-frequency generation and Ferroelectric-like Switching in Si-O Polar Structures
(2009-01-01)
Shieh, Jia-Min
;
Yu, Wen-Chien
;
Huang, Jung Y.
;
Wang, Yi-Chao
;
Chen, Ching-Wei
Optical sum-frequency generation and ferroelectric-like switching in Si-O polar structures comprised of Si nanocrystals (nc-Si) in mesoporous silica was reported and attributed to polar layers lying at the interfaces between one-side bonded nc-Si and host. (C) 2009 Optical Society of America
Room-temperature crystallization of amorphous silicon by near-UV femtosecond pulses
(2020-05-01)
Pan, Ci-Ling
;
Chen, Kuan-Wen
;
Wang, Yi-Chao
;
Kao, Shih-Hsuan
;
Wu, Pohsun
Near ultraviolet (lambda approximate to 400 nm) femtosecond laser annealing (400 nm-FLA) in a scanning mode was employed to crystallize amorphous silicon (a-Si) films at room temperature. The average grain size of polycrystalline silicon annealed was studied as a function of the incident laser fluence and beam overlap or the number of laser shots irradiated. In general, the grain size can be enlarged by either increasing the beam overlap at a fixed laser fluence or increasing the laser fluence for a fixed number of laser shots. An apparent threshold for the onset of rapid enlargement of grain size was observed for processing at similar to 90% overlap and fluences above 25 mJ/cm(2). A maximum grain size of similar to 280 nm was attained at a laser fluence of 30 mJ/cm(2) and overlap of 93.75%, beyond which the grain size attained was smaller, and eventually, ablation was observed at an overlap of 97.5% and higher. These trends and observed surface morphology of annealed samples suggest that the crystallization mechanism is like sequential lateral solidification, similar to 800 nm-FLA and excimer laser annealing. Raman spectroscopic studies show that the degree of crystallization achieved with 400 nm-FLA is even higher than that of 800 nm-FLA. Cross-sectional scanning electron microscopic images indicate that the 100 nm-thick a-Si film is not fully crystallized. This can be explained by the much shorter penetration depth of 400 nm light than that of 800 nm light in a-Si.
THz time-domain spectroscopic studies of a ferroelectric liquid crystal in the SmA* and SmC* phases
(2008)
Tang, Tsung-Ta
;
Pan, Ru-Pin
;
Wang, Yi-Chao
;
Pan, Ci-Ling
;
電子物理學系
We report complex refractive indices of a ferroelectric liquid crystal (FLC) ZLI-4654-000 from 0.3 to 3.0 THz by THz time-domain Spectroscopy. Extraordinary and ordinary refractive indices of this FLC in the SmA* phase (67.9 degrees C) as well as the SmC* phase (58.1 degrees C) are determined. The birefringence of the FLC varies with frequency but is comparable to its value in the visible, 0.13, while the imaginary indices of refraction in both phases are <= 0.06. Absorption bands are found for ordinary waves in both phases and e-waves in SmA* phases.