Pump polarization dependent ultrafast carrier dynamics and two-photon absorption in an a-plane ZnO epitaxial film

Abstract

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.