Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 81: Oxides and Insulator Surfaces I
O 81.9: Talk
Thursday, March 10, 2016, 12:45–13:00, H4
Electronic structure of ultra-thin ZnO on Metal substrates — •Bjoern Bieniek1, Patrick Rinke2, Oliver T. Hofmann3, and Matthias Scheffler1 — 1Fritz-Haber-Institut der MPG, Berlin, Germany — 2Aalto University, Helsinki, Finland — 3TU Graz, Austria
ZnO is a promising candidate for applications in opto-electronics. For a successful application stable n-type and p-type ZnO would be needed. As for many wide band gap semi-conductors, p-type conductivity is difficult to achieve in ZnO. We propose ZnO ultra-thin films on metal substrates as model systems for investigating p-type conductivity in ZnO. In our investigation of the electronic structure of ultra-thin ZnO films (1 to 4 layers) on the (111) surfaces of Ag, Cu, Pd, Pt, Ni, and Rh by means of DFT with the PBE and HSE06 exchange-correlation functionals we find a novel mechanism to achieve p-type conductivity at the surfaces of ZnO thin films on metal substrates. This mechanism is based on the intrinsic polar nature of ZnO (0001) films. With increasing thickness the polar character of wurtzite ZnO emerges as the films structurally transform from α-BN to wurtzite. electrons are transferred from the Zn-terminated interface to adjacent layers. The resulting field shifts the electronic states upwards until the Fermi energy, provided by the metal, is reached and the film becomes effectively p-type doped at its surface by pinning the electronic states of the top most layer(s) at the Fermi level. The number of layers necessary to achieve effective p-type doping depends on the metallic substrate. We also discuss intrinsic defects in the ZnO films on metal substrates.