Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 10: Semiconductor Substrates: Epitaxy and Growth

O 10.1: Talk

Monday, February 25, 2008, 13:15–13:30, MA 042

Thickness-dependent structural investigation of thin GaN films by Photoelectron Diffraction — •Christoph Raisch, Alexey Sidorenko, Heiko Peisert, and Thomas Chassé — University of Tübingen, Institute of Physical Chemistry

Thin films of hexagonal gallium nitride have been grown on 6H-SiC by ion-beam assisted MBE. The thickness ranges from submonolayers to bulk-like samples of more than 100 monolayers. The samples were characterised by XPS, LEED and XPD. During growth, two different types of wetting layers were observed (i) a Ga metal wetting layer on the SiC substrate and (ii) a Ga metal wetting layer on top of the growing GaN film. They prove essential for the spreading wetting growth mechanism and were used to derive interface electronic parameters of the Ga/SiC and Ga/GaN Schottky barriers.

The substrate and the films have been examined by x-ray photoelectron diffraction XPD, a method capable of determining the local atomic structure of crystalline materials. By choosing different photoemission lines, the environments of gallium and nitrogen have been investigated separately and are compared to each other. The differences between Ga2p and Ga3d emission have been evaluated, with Ga3d photoelectrons being bulk sensitive while Ga2p photoelectrons are probing the surface. Features evolving with thickness are identified and interpreted. The experiments are supported by multiple scattering cluster calculations, showing clear trends with increasing film thickness. The simulations also allow the determination of the polarity of the films, which is found to be Ga-terminated for all samples.