A scanning tunnelling microscopic imaging and spectroscopic study was made of a highly p-doped wide-bandgap semiconducting 4H-SiC(00•1) surface. Whereas n- and p-doped 6H-SiC or n-doped 4H-SiC surfaces could be relatively easily imaged with a scanning tunnelling microscopy, the p-doped 4H-SiC could not be imaged due to the absence of any surface conductivity. This was considered to be surprising, given the presence of a p-doped degenerate epitaxial layer. The behaviour could be explained by the formation of a Schottky barrier either between the tip and the surface or between the surface and the sample holder; depending upon the polarity of the applied voltage. It was found that prolonged and repeated exposure of the SiC surface to a Si atomic flux, followed by thermal annealing, were required before the surface conductivity was sufficient to allow scanning tunnelling microscopic images to be recorded. The result was the deposition of overlayers of Si, with structures similar to Si(111) 7 x 7, Si(113) 3 x 2, and Si(110) 16 x 2 rather than the expected stable SiC(0001) 3 x 3 reconstruction. Also demonstrated was the ability of scanning tunnelling spectroscopy to distinguish between the Si and the SiC phases; based upon the difference in their band-gaps.

Scanning Tunnelling Microscopy Imaging and Spectroscopy of p-Type Degenerate 4H-SiC(0001). A.Laikhtman, G.Baffou, A.J.Mayne, G.Dujardin: Journal of Physics - Condensed Matter, 2005, 17[26], 4015-22