Dresden 2009 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
HL: Fachverband Halbleiterphysik
HL 36: ZnO: preparation and characterization II
HL 36.1: Vortrag
Mittwoch, 25. März 2009, 14:00–14:15, POT 51
Ultrafast exciton dynamics of highly excited ZnO — •Jan-Peter Richters1, Tina Shih2, Jürgen Gutowski1, and Tobias Voss1 — 1Institute of Solid State Physics, University of Bremen, P.O. Box 330440, D-28334 Bremen — 2School of Engineering and Applied Sciences and Department of Physics, Harvard University, Cambridge, MA, USA
Large band-gap semiconductors like ZnO are currently of great interest as light emitting material and lasing media in the blue-UV spectral range. In order to make use of these materials it is mandatory to understand the charge carrier dynamics and excitonic effects at high excitation densities.
We present results of pump-probe reflectance spectroscopy of c-plane and m-plane ZnO bulk material with a temporal resolution of Δ t < 200 fs. The sample is excited using a frequency tripled (266 nm) Ti:Sapphire laser. The white light probe pulse (300 nm < λprobe < 600 nm) is generated by converting the Ti:Sapphire pulse with a CaF2 crystal. We analyze the results of the reflectivity measurements by use of an exciton polariton model, from which we can obtain damping, shift, and broadening of the exciton resonances. For excitation densities near to the damage threshold of ZnO, the resonance is completely bleached on a time scale of several tens of ps. Our results indicate that lasing in ZnO observed under high excitation densities using fs-lasers is most probably not an excitonic process, but needs to be described in the frame of a strongly Coulomb correlated electron-hole plasma.