Browsing by Author "Hsu, Wei-Tse"

Now showing 1 - 3 of 3

Raman study of alloy potential fluctuations in MgxZn1-xO nanopowders
(2007-05-09)
Pan, Ching-Ju
;
Lin, Kuo-Feng
;
Hsu, Wei-Tse
;
Hsieh, Wen-Feng
;
光電工程學系
The blueshift of near-band-edge emission and excitonic absorption indicate that Zn2+ ions are successfully substituted by Mg2+ ions in MgxZn1-xO nanopowders for 0 <= x <= 0.14. The changes in Raman spectral linewidth and the asymmetry of the E-2 ( high) mode for various Mg contents can be well described by a modified spatial correlation model that considers the grain size distribution. With increasing Mg concentration, the alloy potential fluctuations lead to a decrease in the grain size, which is induced by the surplus Mg2+ that could form MgO clusters surrounding the crystalline MgZnO.
Reducing exciton-longitudinal optical phonon coupling with increasing Mg incorporation in MgZnO powders
(2007-12-15)
Pan, Ching-Ju
;
Lin, Kuo-Feng
;
Hsu, Wei-Tse
;
Hsieh, Wen-Feng
;
光電工程學系
The coupling between exciton and longitudinal optical (LO) phonon was investigated in the use of temperature-dependent photoluminescence from Mg(x)Zn(1-x)O powders prepared by a sol-gel method in the range of 0 <= x <= 0.05. The exciton binding energy increases to 73 meV for 5 at. % Mg incorporated powders. The strength of exciton-LO phonon coupling was deduced from the energy shift of exciton emission with temperature variation. The increase of the exciton binding energy results from a decrease of the exciton Bohr radius that is responsible for reducing the coupling strength of exciton-LO phonon as increasing Mg content. (c) 2007 American Institute of Physics.
Reducing exciton-longitudinal-optical phonon interaction with shrinking ZnO quantum dots
(2007-10-29)
Hsu, Wei-Tse
;
Lin, Kuo-Feng
;
Hsieh, Wen-Feng
;
光電工程學系
;
Department of Photonics
The exciton-longitudinal-optical-phonon (LO-phonon) interaction was observed to decrease with reducing ZnO particle size to its exciton Bohr radius (a(B)). The unapparent LO-phonon replicas of free exciton (FX) emission and the smaller FX energy difference between 13 and 300 K reveal decreasing weighting of exciton-LO phonon coupling strength. The diminished Frohlich interaction mainly results from the reducing a(B) with size due to the quantum confinement effect that makes the exciton less polar. (C) 2007 American Institute of Physics.