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Exciton Localization of High-Quality ZnO/MgxZn1-x Multiple Quantum Wells on Si (111) with a Y2O3 Buffer Layer
(2018-08-01)
Liu, Wei-Rein
;
Huang, Wei-Lun
;
Wu, Yung-Chi
;
Lai, Liang-Hsun
;
Hsu, Chia-Hung
We report the structural and optical properties of ten-period ZnO/MgxZn1-x multiple quantum wells (MQWs) prepared on the most widely used semiconductor material, Si. The introduction of a nanometer thick high-k Y2O3 transition layer between Si (111) substrate and a ZnO buffer layer significantly improves the structural perfection of the MQWs grown on top of it. The high structural quality of the ZnO/MgxZn1-xO MQWs is evidenced by the appearance of pronounced high order satellite peaks in X-ray crystal truncation rods; high resolution cross-sectional transmission electron microscopy images also confirmed the regularly arranged well and barrier layers. When the well width is less than similar to 2.7 nm, the quantum-confined Stark effect in MQWs can be negligible. Not only the increasing exciton-binding energy but also reducing exciton-phonon coupling determined in temperature-dependent photoluminescence spectra indicate quantum-size effect. Our results demonstrate that ZnO/MgxZn1-xO MQWs integrated on Si have great potential in UV optoelectronic device applications.
Influence of basal stacking faults on luminescence of m-plane Mg0.19Zn0.81O/ZnO quantum wells grown on a two-step MgZnO-buffer layer
(2019-03-01)
Wu, Yung-Chi
;
Chang, Ning-An
;
Yang, Tsung-Han
;
Tsai, Chih-Ya
;
Chen, Hou-Ren
Different well widths of m-plane Mg0.19Zn0.81O/ZnO multiple quantum wells (MQWs) have been fabricated on the two-step pregrown MgZnO-buffered m-plane sapphires by a pulsed laser deposition and have a narrower linewidth on x-ray diffraction than ZnO-buffered MQWs. By using the variation method to calculate the band diagram and by corroborating the results of temperature-dependent photoluminescence, we confirm the binding energies of free exciton and basal-stacking-fault-bound exciton, which is composed of electrons in the barrier and confined hole in the narrow-width MQWs. The coupling of A1(LO) phonon with excitons in m-MQWs shows more sensitivity toward a decrease in well width than E2(low), due to the crystal symmetry and the reduced Bohr radius. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)
Coherent acoustic phonon oscillation accompanied with backward acoustic pulse below exciton resonance in a ZnO epifilm on oxide-buffered Si(111)
(2016-08-17)
Lin, Ja-Hon
;
Shen, Yu-Kai
;
Liu, Wei-Rein
;
Lu, Chia-Hui
;
Chen, Yao-Hui
Unlike coherent acoustic phonons (CAPs) generated from heat induced thermal stress by the coated Au film, we demonstrated the oscillation from c-ZnO epitaxial film on oxide buffered Si through a degenerate pump-probe technique. As the excited photon energy was set below the exciton resonance, the electronic stress that resulted from defect resonance was used to induce acoustic wave. The damped oscillation revealed a superposition of a high frequency and long decay CAP signal with a backward propagating acoustic pulse which was generated by the absorption of the penetrated pump beam at the Si surface and selected by the ZnO layer as the acoustic resonator.
The optical property of vertical external cavity surface-emitting laser
(2015)
Wu, Yung-Chi
;
Lin, Da-Wei
;
Hsieh, Wen-Feng
;
Lan, Yu-Pin
;
光電工程學系
Under passive Q-switched laser pumping, a vertical-external-cavity surface-emitting laser consisted of a semiconductor gain medium with a high reflectivity dielectric distributed Bragg reflection and an external mirror can achieve ultra-low threshold lasing at room temperature.
The influence of tetrapod-like ZnO morphology and electrolytes on energy conversion efficiency of dye-sensitized solar cells
(2010-12-01)
Lee, Chia-Hua
;
Chiu, Wei-Hao
;
Lee, Kun-Mu
;
Yen, Wen-Hsiang
;
Lin, Hsiu-Fen
Tetrapod-like ZnO nanostructures prepared by dc plasma technology were used as photoelectrodes in dye-sensitized solar cells (DSSCs) Each of the tetrapod-like ZnO possesses four extended arms that offer improved electron transport properties Tetrapod-like ZnO with short (S-ZnO) and long arms (L-ZnO) were synthesized by controlling the plasma gas flow and the input power Between these two tetrapod-like ZnO nanopowders the DSSCs using S-ZnO showed higher energy conversion efficiency than using L-ZnO This is due to the resulting increase in dye adsorption and enhanced short-circuit current density using S-ZnO Electrochemical Impedance spectroscopy (EIS) shows that the properties of electron transport of S-ZnO are superior to that of the L-ZnO We investigated the effect of the redox electrolytes (12) and the additives (Lil and TBP) on the performance of the DSSCs by intensity-modulated photovoltage spectroscopy and EIS (C) 2010 Elsevier Ltd All rights reserved
Exciton-polaritons study in ZnO-based hybrid microcavities
(2012)
Lan, Yu-Pin
;
Lai, Ying-Yu
;
Huang, Si-Wei
;
Chen, Jun-Rong
;
Wu, Yung-Chi
The characteristics of exciton-polaritons in ZnO-based microcavities (MCs) are demonstrated with a large vacuum Rabi splitting due to large exciton binding energy and oscillator strength. The lower polariton branches (LPBs) can be clearly observed. For low temperature and large negative detuning conditions, a clear polariton relaxation bottleneck in bulk ZnO-based MCs has been observed in angle-resolved photoluminescence measurements from 100 to 353 K at different cavity-exciton detunings. The bottleneck is strongly suppressed with increasing the temperature and pumping power and reducing detuning. This observed results supposed to be due to more efficient phonon-assisted relaxation and a longer radiative lifetime of the polaritons. In addition, the linewidth broadening, blue-shift of the emission peak, and polarization of polariton lasing from below threshold to up threshold are also discussed.
Carrier dynamics of thin ZnO epifilm above band-gap states
(2009)
Ou, Po-Chi
;
Lin, Ja-Hon
;
Chang, C. A.
;
Liu, W. R.
;
Hsieh, Wen-Feng
Ultrafast carrier dynamics of ZnO epifilm were investigated by the pump probe meausrement Relative fast occruring and recovery of band gap renormalizaion following the band filling effect will result in transmission change at 362 nm.
Structural and optical properties of ZnMgO nanostructures formed by Mg in-diffused ZnO nanowires
(2007-04-01)
Pan, Ching-Ju
;
Hsu, Hsu-Cheng
;
Cheng, Hsin-Ming
;
Wu, Chun-Yi
;
Hsieh, Wen-Feng
ZnMgO nanostructures with wurtzite phase were prepared by thermal diffusion of Mg into the ZnO nanowires. As ZnO light-emitting devices have been operated by using ZnMgO layers as energy barrier layers to confine the carriers, it is essential to realize the characterization of ZnMgO particularly. In this work, the Mg content in Zn1-xMgxO alloy determined by X-ray diffraction (XRD) and photoluminescence (PL) shows a good coincidence. The variation of lattice constant and the blueshift of near-band-edge emission indicate that Zn2+ ions are successfully substituted by Mg2+ ions in the ZnO lattice. In Raman-scattering studies, the change of E-2(high) phonon line shape in ZnO:Mg nanostructures reveals the microscopic substitutional disorder. In addition to the host phonons of ZnO, two additional bands around 383 and 510cm(-1) are presumably attributed to the Mg-related vibrational modes. (C) 2007 Elsevier Inc. All rights reserved.

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