Browsing by Author "Ou, Po-Chi"

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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.
Thickness effect on ultrafast thermalization of carriers in above-band-gap states in ZnO epitaxial films
(2010-12-15)
Ou, Po-Chi
;
Lin, Ja-Hon
;
Chang, Chi-An
;
Liu, Wei-Rein
;
Hsieh, Wen-Feng
Energy-dependent free-carrier dynamics was investigated in 70 nm (thin) and 1 mu m (thick) ZnO epifilms using the optical pump-probe technique. The far-above-band-gap dynamics in the thin epifilm reveals the prolonged relaxation and the slow recovery of renormalized band gap. The band-gap renormalization (BGR) effect is affected by the inefficient carrier-phonon scattering. In addition, the loss of excited carrier density via surface trapping results in an energy-dependent BGR buildup time. However, the far-above-band-gap dynamics in the thick epifilm reveals fast relaxation followed by BGR recovery, which is independent of the photon energy. The near-band-gap dynamics shows an ultrafast carrier thermalization both in the thin and the thick epifilms.
Ultrafast relaxation and absorption saturation at near exciton resonance in a thin ZnO epilayer
(2011-01-01)
Ou, Po-Chi
;
Liu, Wei-Rein
;
Ton, Ho-Jei
;
Lin, Ja-Hon
;
Hsieh, Wen-Feng
We observed ultrafast free exciton thermalization time of 700-900 fs and obtained the magnitude of maximal differential absorption to be 1.8 x 10(4) cm(-1) with the pumping fluence of 10 mu J/cm(2) by measuring transient differential transmission in a thin ZnO epitaxial layer at room temperature. The largest induced transparency occurs near exciton resonance associated with absorption saturation by comparing the excitation from the above band-gap to band-tail states. The pumping dependent transient absorption reveals transition of excitonic relaxation from exciton-phonon scattering to exciton-exciton scattering or to an electron-hole plasma. (C) 2011 American Institute of Physics. [doi:10.1063/1.3525993]