A PHOTOEMISSION-STUDY OF 4H-SIC(0001)

A photoemission study using synchrotron radiation of the (0001) surfac e of 4H-SiC is reported. The investigations were concentrated on the ( root 3 x root 3)-R30 degrees and (6 root 3 x 6 root 3)-R30 degrees rec onstructed surfaces, prepared by resistive heating at a temperature of about 1000 degrees C and 1250 degrees C. respectively. Results from s urfaces heated at intermediate temperatures, exhibiting a mixture of t hese reconstructions, and after heating at a higher temperature, when graphitisation is clearly observed, are also presented. The root 3 and 6 root 3 reconstructed surfaces exhibit characteristic core level and valence band spectra. High resolution core level spectra show unambig uously the presence of surface shifted components in both the Si 2p an d C Is core levels. For the root 3 reconstruction, two surface shifted components are observed both in the Si 2p and C Is level. For the 6 r oot 3 reconstruction, the surface region is found to contain a conside rably larger amount of carbon. This carbon is found not to be graphiti c since surface C Is components with binding energies different from a graphitic C Is peak are observed. Graphitisation, as revealed by the appearance of a graphitic C Is peak, is observed only after heating to a higher temperature than that required for obtaining a well develope d root 3 diffraction pattern.