Browsing by Author "Su, Hsing-Jung"

Now showing 1 - 2 of 2

Pump polarization dependent ultrafast carrier dynamics and two-photon absorption in an a-plane ZnO epitaxial film
(2015-10-05)
Lin, Ja-Hon
;
Su, Hsing-Jung
;
Lu, Chia-Hui
;
Chang, Chun-peng
;
Liu, Wei-Rein
The ultrafast carrier dynamics of non-polar a-plane ZnO epi-film, with the energy difference between the A- and C-valence bands of about 23 meV, grown on r-plane sapphire were investigated using the reflection type pump-probe technique under two perpendicular polarized pumps. By exciting the electron from A-valence band through pump pokuization perpendicular to the c-axis of a-ZnO (E-pu perpendicular to c), the TDR trace revealed two photon absorption (TPA), hand filling (BF) and bandgap renormalization (BGR) effects that can be reasonably explained by the electron dynamics in the conduction band. By exciting the electron from C-valence band through parallel pump polarization (E-pu parallel to c), only the BF effect was observed in the TDR trace owing to the hole dynamics in the valence hands. The occurrence of TPA was determined by the pump efficiency depending on the energy difference between the pump photon and the intermediate exciton resonance state. (C) 2015 AIP Publishing LLC.
Room temperature excitonic dynamics of non-polar a-plane ZnO epifilms
(2016-09)
Lin, Ja-Hon
;
Liu, Wei-Rein
;
Lin, Yi-Chin
;
Su, Hsing-Jung
;
Chen, Hou-Ren
Pump polarization dependent carrier dynamics, particularly excitonic dynamics, of non-polar a-plane zinc oxide (ZnO) epifilms with two different thicknesses were investigated using time resolved measurements. Unlike the electron and hole dynamics through the above-bandgap excitation, transient differential reflectance (TDR) traces revealed similar trends under two orthogonal pump polarization conditions relative to the c-axis (E-pu +/- c and E-pu vertical bar vertical bar c) of a-ZnO around near-exciton-resonance excitation. By means of a band diagram, the bandgap renormalization (BGR) effect can be reasonably explained by the screening of the Coulomb potential energy due to the accumulation of relaxed free carriers that were initially excited through the absorption of two cascaded pump photons via the excitonic level, a process known as two photon absorption (TPA). Thus, the modulation depths of the TPA around zero time delay, due to simultaneous absorption of one pump and one probe photon via the excitonic level, increased linearly with the pump fluence, proportional to the modulation depth resulting from the BGR effects. (C) 2016 Author(s).