Evidence for photogenerated intermediate hole polarons in ZnO
Sezen, H. / Shang, H. / Bebensee, F. / Yang, C. / Buchholz, M. / Nefedov, A. / Heissler, S. / Carbogno, C. / Scheffler, M. / Rinke, P. / Wöll, C. (2015)
Nature Communications (2015) 6, 6901 doi:10.1038/ncomms7901
- Datum: April 2015
Despite their pronounced importance for oxide-based photochemistry, optoelectronics and photovoltaics, only fairly little is known about the polaron lifetimes and binding energies. Polarons represent a crucial intermediate step populated immediately after dissociation of the excitons formed in the primary photoabsorption process.
Here we present a novel approach to studying photoexcited polarons in an important photoactive oxide, ZnO, using infrared (IR) reflection–absorption spectroscopy (IRRAS) with a time resolution of 100 ms. For well-defined (10-10) oriented ZnO single-crystal substrates, we observe intense IR absorption bands at around 200 meV exhibiting a pronounced temperature dependence. On the basis of first-principles-based electronic structure calculations, we assign these features to hole polarons of intermediate coupling strength.