Browsing by Author "Sun, Greg"

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Fabrication and characteristics of GaN/AlGaN multilayer structure for terahertz quantum-cascade laser
(2006)
Wang, S. C.
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Soref, Richard
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Sun, Greg
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光電工程學系
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Department of Photonics
The GaN/AlGaN multilayer structure for the active regions of terahertz quantum cascade lasers (QCLs) was grown by metal organic chemical vapor deposition (MOCVD). The surface morphology of the grown sample showed good surface quality with an average roughness of less than 1 nm. The x-ray diffraction pattern and transmission electron microscopy images showed that the well-controlled quantum cascade GaN/AlGaN layers were grown. The Fourier transform infrared spectrometer measurement showed a distinct A(1) (LO) phonon frequency at 822 cm(-1) that is red-shifted with respect to the single Al0.2Ga0.8N layer due to the good periodicity of the grown quantum cascade GaN/Al0.2Ga0.8N structure. MOCVD growth should be a viable technique for fabrication of AlGaN/GaN quantum cascade laser and phonon frequency shift should be a key indicator for the good periodicity of the grown QCL structure.
GaN/AlGaN active regions for terahertz quantum cascade lasers grown by low-pressure metal organic vapor deposition
(2007-01-01)
Huang, G. S.
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Lu, T. C.
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Yao, H. H.
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Kuo, H. C.
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Wang, S. C.
The GaN/AlGaN active regions for terahertz (THz) quantum cascade lasers were grown by metal organic chemical vapor deposition (MOCVD). The surface of the sample was characterized by atomic force microscopy (AFM). The structure of this sample was evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern and cross-sectional TEM images showed that a well-controlled quantum cascade GaN/AlGaN layers could be prepared. Optical properties of the active region of a terahertz GaN/AlGaN have been investigated by Fourier transform infrared (FTIR) spectrometer. It was found that the frequency of E-1(LO) phonon decreased in quantum cascade GaN/AlGaN structures. The phonon frequency shift could be attributed to the effect of phonon zone folding. (c) 2006 Elsevier B.V. All rights reserved.
Second Harmonic Light Manipulation with Vertical Split Ring Resonators
(2019-02-15)
Tsai, Wei-Yi
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Chung, Tsung Lin
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Hsiao, Hui-Hsin
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Chen, Jia-Wern
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Lin, Ren Jie
The second harmonic generation (SHG) of vertical and planar split-ring resonators (SRRs) that are broken centro-symmetry configurations at the interface of metal surface and air is investigated. Strong interactions, better electromagnetic field confinements, and less leakage into the substrate for vertical SRRs are found. Experimental results show a 2.6-fold enhancement of SHG nonlinearity, which is in good agreement with simulations and calculations. Demonstrations of 3D metastructures and vertical SRRs with strong SHG nonlinearity majorly result from magnetic dipole and electric quadrupole clearly provides potential applications for photonics and sensing.