Browsing by Author "Lin, Yung-Hsiang"

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Characteristics of Blue GaN/InGaN Quantum-Well Light-Emitting Transistor
(2020-01-01)
Lan, Hao-Yu
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Tseng, I-Chen
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Lin, Yung-Hsiang
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Chang, Shu-Wei
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Wu, Chao-Hsin
We demonstrate simultaneous electrical and optical modulations of the first GaN/InGaN quantum-well light-emitting transistor (QW-LET) which contains an In-0.15 Ga0.85N QW in the heavily p-doped In-0.05 Ga0.95N base. Unlike GaAs/InGaAs counterparts, the GaN/InGaN QW- LET has a current gain (up to 5) and optical power which increases linearly with the base current. Its emission spectra are centered at a wavelength of 420 nm and barely shift with the current injection, in contrast to the behavior of typical nitride-based LEDs. The unusual features of this device may be related to the tilted band profile induced by the polarization field in the QW and issue of p-type doping.
Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions
(2016-01-22)
Cheng, Chih-Hsien
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Tzou, An-Jye
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Chang, Jung-Hung
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Chi, Yu-Chieh
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Lin, Yung-Hsiang
The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC1-x) buffer is demonstrated. The a-SixC1-x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC1-x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of SixC1-x buffer. The C-rich SixC1-x favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the SixC1-x buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Sirich SixC1-x buffer, the device deposited on C-rich SixC1-x buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively.
Inferring Distant-Time Location in Low-Sampling-Rate Trajectories
(2013-01-01)
Chiang, Meng-Fen
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Lin, Yung-Hsiang
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Peng, Wen-Chih
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Yu, Philip S.
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資訊工程學系
With the growth of location-based services and social services, low sampling-rate trajectories from check-in data or photos with geotag information becomes ubiquitous. In general, most detailed moving information in low-sampling-rate trajectories are lost. Prior works have elaborated on distant-time location prediction in highsampling-rate trajectories. However, existing prediction models are pattern-based and thus not applicable due to the sparsity of data points in low-sampling-rate trajectories. To address the sparsity in low-sampling-rate trajectories, we develop a Reachability-based prediction model on Time-constrained Mobility Graph (RTMG) to predict locations for distant-time queries. Specifically, we design an adaptive temporal exploration approach to extract effective supporting trajectories that are temporally close to the query time. Based on'the supporting trajectories, a Time-constrained mobility Graph (TG) is constructed to capture mobility information at the given query time. In light of TG, we further derive the reachability probabilities among locations in TG. Thus, a location with maximum reachability from the current location among all possi ble locations in supporting trajectories is considered as the prediction result. To efficiently process queries, we proposed the index structure Sorted Interval-Tree (SOIT) to organize location records. Extensive experiments with real data demonstrated the effectiveness and efficiency of RTMG. First, RTMG with adapthie temporal exploration significantly outperforms the existing pattern-based prediction model HPM [2] over varying data sparsity in terms of higher accuracy and higher coverage. Also, the proposed index structure SOIT can efficiently speedup RTMG in large-scale trajectory dataset. In the future, we could extend RTMG by considering more factors (e.g., staying durations in locations, application usages in smart phones) to further improve the prediction accuracy.
Mining Top-K Relevant Stay Regions from Historical Trajectories
(2014-01-01)
Lin, Yung-Hsiang
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Lai, Chien-Hsiang
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Lei, Po-Ruey
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資訊工程學系
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Department of Computer Science
With increasingly prevalent mobile positioning devices, such as GPS loggers, smart phones, and GPS navigation devices, a huge amount of trajectories data is collected. Users are able to obtain the various location-based services by uploading their trajectories. In this paper, we address that a user\'s movement behavior is able to discover by their similar shape trajectories and resulted in some regions frequently stay in common, called relevant stay regions. Once a set of stay regions discovered, we can predict the next region where the user intends to go and provide location-based information of the next stay in advance, such as traffic status, targeted advertises, sightseeing recommendations, and so on. Prior works have elaborated on discovering stay region from the whole crowd trajectories and then exploring the relations between the regions to describe the movement patterns for location prediction. However, the trajectories pass the same region may not have the similar movement behavior. Thus, we propose a framework to discover stay regions relevant to the specific movement behavior and then applied in location prediction, called Region Modeling and Mobility Prediction. The proposed framework includes two modules: region modeling and mobility prediction. In the region modeling module, we develop shape clustering method to group the similar trajectories from historical data and then explore the stay region model from trajectory clusters. Based on the discovered region model, the mobility prediction module provide a cluster selection algorithm and several prediction strategies to generate the top-k relevant stay regions. Experiments results on real datasets demonstrate the effectiveness and accuracy of our proposed model on detecting next stay region, comparing with other baseline methods.
Nonstoichiometric SiC Bus/Ring Waveguide Based All-Optical Data Format Follower and Inverter
(2016-05)
Su, Sheng-Pin
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Wu, Chung-Lun
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Cheng, Chih-Hsien
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Huang, Bo-Ji
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Wang, Huai-Yung
Nonstoichiometric silicon carbide (SiC) bus/ring waveguide resonator based all-optical data-format follower and inverter is demonstrated to perform ultrafast dual functional wavelength and data-format conversion. The buried Si quantum dots (Si-Qps) with strong quantum confinement effect effectively result in a significant change on the nonlinear refractive index of 3.14 X 10(-1)3 cm(2)/W, which induces a red shift of 0.07 nm on the resonant wavelength comb of the nonstoichiometric SiC ring waveguide resonator. By injecting the 12 Gbit/s optical pulsed return-to-zero on-off keying (PRZ-OOK) data stream into the ring waveguide at a notched wavelength of 1551.08 nm, the induced red-shift on resonant wavelengths allows versatile all-optical data processing functions, including data wavelength conversion and data format following/inversion, on the data patterns transferred to the probe. The eye-opening diagram analysis at 12 Gbit/s reveals that the data transferred to the probe can provide a signal-to-noise ratio of 9.4 dB, and a receiving power penalty is degraded by 2.6 dB as compared to that of the pump data.
Strong optical nonlinearity of the nonstoichiometric silicon carbide
(2015-01-01)
Cheng, Chih-Hsien
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Wu, Chung-Lun
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Lin, Yung-Hsiang
;
Yan, Wen-Long
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Shih, Min-Hsiung
Enhanced nonlinear refractive indices and absorption coefficients of nonstoichiometric SixC1-x with varying C/Si composition ratios from 0.51 to 1.83 grown by low-temperature plasma-enhanced chemical vapor deposition are demonstrated. When increasing the [CH4]/[CH4 + SiH4] fluence ratio from 70% to 92%, two Raman scattering signals at 795 and 970 cm(-1) contributed by transverse and longitudinal optical modes of Si-C bonds are simultaneously enhanced in stoichiometric and C-rich SixC1-x samples, whereas the Si-associated Raman peak at 520 cm(-1) decreases with increasing C/Si composition ratio. The C-rich SixC1-x film shows additional Raman scattering peaks at 1330 and 1580 cm(-1), which are individually contributed by the diamond-like C-C bonds and the G peak of the graphite-like C-C bonds, respectively. The nonlinear refractive index increases to 1 +/- 0.1 x 10(-11) cm(2) W-1 upon increasing the C/Si composition ratio up to 1.83, which is four orders of magnitude higher than that of bulk SiC. The increased C/Si composition ratio reduces the lattice constant and the effective mass of the SixC1-x film and enhances its nonlinear refractive index effectively. In comparison with the sp(3)-orbital C-C bond, the sp(2)-orbital C-C bond in SixC1-x films dominates the enhancement of nonlinear refractive index. By contrast, the nonlinear absorption coefficient changes sign and decreases magnitude when transferring the SixC1-x film from Si-rich to C-rich conditions. This sign reversal is primarily attributed to the conversion in the absorption mechanism from two-photon absorption to nonlinear saturable absorption. Unlike Si-Si bonds which favor two-photon absorption, the sp(2)-orbital C-C bonds with delocalized pi-electrons essentially enhance the saturable absorbance. Hence, a higher nonlinear refractive index and a higher saturable absorption coefficient can be obtained by enriching the sp(2)-orbital C-C bonds in C-rich SixC1-x films.