Browsing by Author "Yaseen, Mohammad Tariq"

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Near infrared to UV dielectric functions of Al doped ZnO films deposited on c-plane sapphire substrate using pulsed laser deposition
(2013-11-01)
Thangavel, R.
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Yaseen, Mohammad Tariq
;
Chang, Yia Chung
;
Hsu, Chia-Hao
;
Yeh, Kuo-Wei
Transparent conducting polycrystalline Al-doped ZnO (AZO) films were deposited on sapphire substrates at substrate temperatures ranging from 200 to 300 degrees C by pulsed laser deposition (PLD). X-ray diffraction measurement shows that the crystalline quality of AZO films was improved with increased substrate temperature. The electrical and optical properties of the AZO films have been systematically studied via various experimental tools. The room-temperature micro-photoluminescence (mu-PL) spectra show a strong ultraviolet (UV) excitonic emission and weak deep-level emission, which indicate low structural defects in the films. A Raman shift of about 11 cm(-1) is observed for the first-order longitudinal-optical (LO) phonon peak for AZO films when compared to the LO phonon peak of bulk ZnO. The Raman spectra obtained with UV resonant excitation at room temperature show multi-phonon LO modes up to third order. Optical response due to free electrons of the AZO films was characterized in the photon energy range from 0.6 to 6.5 eV by spectroscopic ellipsometry (SE). The free electron response was expressed by a simple Drude model combined with the Cauchy model are reported. (C) 2013 Elsevier Ltd. All rights reserved.
Optimization of High-Q Coupled Nanobeam Cavity for Label-Free Sensing
(2015-10-01)
Yaseen, Mohammad Tariq
;
Yang, Yi-Chun
;
Shih, Min-Hsiung
;
Chang, Yia-Chung
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光電工程學系
We numerically and experimentally investigated the lateral coupling between photonic crystal (PhC) nanobeam (NB) cavities, pursuing high sensitivity and figure of merit (FOM) label-free biosensor. We numerically carried out 3D finite-difference time-domain (3D-FDTD) and the finite element method (FEM) simulations. We showed that when two PhC NB cavities separated by a small gap are evanescently coupled, the variation in the gap width significantly changes the coupling efficiency between the two coupled NB cavities and the resulting resonant frequencies split. Experimentally, we fabricated laterally-coupled PhC NB cavities using (InGaAsP) layer on the InP substrate. For sensing, we showed that the laterally coupled PhC NB cavities sensor exhibits higher sensitivity than the single PhC NB cavity. The higher sensitivity of laterally coupled PhC NB cavities is due to the strong evanescent coupling between nearby PhC NB cavities, which depends on the gap width and it is attributed to the large confinement of the electromagnetic field in the gap (air or liquid). As a result of the lateral coupling, both even (symmetric) and odd (asymmetric) modes exist. We show that even modes are more sensitive than odd modes. In addition, higher-order modes exhibit higher sensitivity. Hence, we characterized and examined the fabricated PhC NB cavity as a label-free biosensor, and it exhibits high figure of merit due to its high Q-factor. This illustrates a potentially useful method for optical sensing at nanoscale.