Browsing by Author "Wu, Kuang-Hsiung"

Now showing 1 - 5 of 5

Improving Crystalline Quality of Non-Vacuum Processed Cu(In,Ga) Se-2 Thin Films by Femtosecond Laser Annealing
(2016)
Li, Jia-Xing
;
She, Nian-Zu
;
Chang, Yu-Hsuan
;
Chen, Shih-Chen
;
Kuo, Hao-Chung
We demonstrate the advantages of femtosecond laser annealing on non-vacuum CIGS thin films. The PL spectra implied some defect-levels or band-fluctuations were eliminated, and the conversion efficiency and ideal factor were enhanced after laser annealing.
Plasmonics in Topological Insulators
(2014-04-16)
Lai, Yi-Ping
;
Lin, I-Tan
;
Wu, Kuang-Hsiung
;
Liu, Jia-Ming
;
電子物理學系
With strong spin-orbit coupling, topological insulators have an insulating bulk state, characterized by a band gap, and a conducting surface state, characterized by a Dirac cone. Plasmons in topological insulators show high frequency-tunability in the mid-infrared and terahertz spectral regions with transverse spin oscillations, also called "spin-plasmons". This paper presents a discussion and review of the developments in this field from the fundamental theory of plasmons in bulk, thin-film, and surface-magnetized topological insulators to the techniques of plasmon excitation and future applications.
Temperature-dependent carrier-phonon coupling in topological insulator Bi2Se3
(2014-12-08)
Lai, Yi-Ping
;
Chen, Hsueh-Ju
;
Wu, Kuang-Hsiung
;
Liu, Jia-Ming
;
電子物理學系
Temperature-dependent (11.0K +/- 294.5 K) carrier-phonon coupling in Bi2Se3 is investigated by ultrafast pump-probe spectroscopy. The rise time of the differential reflectivity is interpreted by a combined effect of electron temperature relaxation and hot-phonon lifetime. The electron-phonon coupling constant of the bulk state (lambda = 0.63 +/- 0.05) is deduced from theoretical fitting. Increasing hot-phonon lifetime with decreasing temperature is attributed to a decreasing phonon-phonon collision rate. A complete analysis of the thermalization process is presented. Understanding carrier and phonon dynamics is essential for future optoelectronic and spintronic applications of topological insulators. (C) 2014 AIP Publishing LLC.
Terahertz optical properties of multilayer graphene: Experimental observation of strong dependence on stacking arrangements and misorientation angles
(2012-12-27)
Lin, I-Tan
;
Liu, Jia-Ming
;
Shi, Kai-Yao
;
Tseng, Pei-Shan
;
Wu, Kuang-Hsiung
The optical conductivity of monolayer and multilayer graphene in the terahertz spectral region is experimentally measured using terahertz time-domain spectroscopy. The stacking arrangement and the misorientation angle of each sample are determined by Raman spectroscopy. The chemical potential of each sample is measured using ultrafast midinfrared pump-probe spectroscopy to be 63 or 64 meV for all samples. The intraband scattering rate can be obtained by fitting the measured data with theoretical models. Other physical parameters, including carrier density, dc conductivity, and carrier mobility, of each sample can also be deduced from the theoretical fitting. The fitting results show the existence of misoriented or AA-stacked layers with an interaction energy of alpha(1) = 217 meV in our multilayer samples. Here we show that the scattering rate strongly depends on the stacking arrangement of the sample. High scattering rates and high optical conductivity are associated with AA-stacked samples, while lower ones are associated with misoriented multilayer graphene. This implies that the THz optoelectronic properties of multilayer graphene can be tuned by purposefully misorienting layers or employing different stacking schemes. DOI: 10.1103/PhysRevB.86.235446 PACS number(s): 78.67.Wj, 61.48.Gh, 72.80.Vp, 73.50.Mx
Terahertz Optoelectronic Property of Graphene: Substrate-Induced Effects on Plasmonic Characteristics
(2014-03-01)
Lin, I-Tan
;
Lai, Yi-Ping
;
Wu, Kuang-Hsiung
;
Liu, Jia-Ming
;
電子物理學系
The terahertz plasmon dispersion of a multilayer system consisting of graphene on dielectric and/or plasma thin layers is systematically investigated. We show that graphene plasmons can couple with other quasiparticles such as phonons and plasmons of the substrate; the characteristics of the plasmon dispersion of graphene are dramatically modified by the presence of the coupling effect. The resultant plasmon dispersion of the multilayer system is a strong function of the physical parameters of the spacer and the substrate, signifying the importance of the substrate selection in constructing graphene-based plasmonic devices.