Disorder beneath epitaxial graphene on SiC(0001): An x-ray absorption study

Abstract

The evolution of silicon carbide ͑0001͒ surface reconstruction upon annealing has been studied by Si K-edge near-edge x-ray-absorption fine structure ͑NEXAFS͒. With the increase in annealing temperature, the fluorescence yield of Si K-edge NEXAFS clearly indicates an increase in disorder of Si atoms in the much deeper interior beneath the surface due to out diffusion of Si atoms to the surface forming increased Si vacancies. The concentration of Si vacancies beneath the epitaxial graphene formed by high-temperature annealing of SiC is estimated to be as high as 15% to a depth of several micrometers. As acceptors in SiC, the high concentration of Si vacancies could have a significant impact on the electronic properties of epitaxial graphene by chargetransfer doping from the substrate and the introduction of interface states.

Microwave-induced nucleation of conducting graphitic domains on silicon carbide surfaces

“…18,34,35 NEXAFS spectroscopy at C and Si K-edges has previously been used to probe the extent of disorder introduced within SiC upon Si sublimation and in epitaxial graphene upon electron bombardment. [36][37][38] Figure 3 depicts C K-edge NEXAFS spectra acquired for the (0001) and (000 1) faces of 6H-SiC. For the C-rich face, a pre-edge resonance is observed at 285.3 eV preceding a strong white line absorption feature at 289.1 eV, which is characteristic of a carbidic linkage.…”

Si clusters on reconstructed SiC (0001) revealed by surface extended x-ray absorption fine structure

“…The near edge spectra of Si K edges are consistent with previous reports. 21,27,28 In the extended region, distinct oscillations are observed for the different surface reconstructions.…”

“…21 These outdiffused Si atoms must contribute to the formation of Si clusters on the surface, especially for the 6 ͱ 3 ϫ 6 ͱ 3R30°recon-structed C rich surface. At around 1200-1300°C when EG is formed, Si atoms will continue to outdiffuse from the bulk.…”

“…21 Therefore, we used Auger yield to measure EXAFS spectra. Although measurement was made on EG, no reasonable spectrum was obtained due to the fact that Si Auger electrons are too surface sensitive for this C-terminated surface to deliver enough count rates.…”

“…The details about the sample preparation and experimental setup can be found elsewhere. 21 To compare with the experimental data, Si K-edge EXAFS calculations were carried out using the FEFF8 code ͑version 8.20, University of Washington͒. 25 As there are three nonequivalent crystallographic sites of Si in the 6H-SiC unit cell, 26 the calculated EXAFS was performed for all Si atoms and averaged over the three sites.…”