Berlin 2008 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 49: ZnO: Optical properties
HL 49.8: Talk
Thursday, February 28, 2008, 12:30–12:45, ER 164
Asymmetry in the excitonic recombinations and impurity incorporation of the two polar faces of homoepitaxially grown ZnO films — •Joachim Sann1, Stefan Lautenschläger1, Niklas Volbers1, Bruno K. Meyer1, Markus R. Wagner2, Ute Haboeck2, and Axel Hoffmann2 — 11st Physics Institute, Justus-Liebig University Giessen, Heinrich Buff Ring 16, 35392 Giessen, Germany — 2Institute of Solid State Physics, TU Berlin, Hardenbergstr. 38, 10623 Berlin, Germany
Homoepitaxial ZnO layers were grown on O-polar and Zn-polar surfaces of ZnO single crystal substrates by chemical vapour deposition. While the structural properties (surface roughness, rocking curve half width) were within experimental error identical, the optical properties as monitored by photoluminescence (PL) were strikingly different. Four excitonic recombination lines are exclusively found on the O-polar surface. In order to understand the defects involved secondary ion mass spectrometry was employed which clearly demonstrated that the impurity incorporation is substantially higher on the O-polar surface. Temperature and power dependent PL measurements provide further insight into the initial-final state recombinations. The newly observed recombinations are caused by excitons bound to a neutral defect complex. In order to account for the thermalisation behaviour found in the temperature dependent measurements splittings in the excited as well as in the ground state must be present. A neutral, isoelectronic Zn vacancy-donor pair is consistent with the experimental data.