Giant reconstruction at the surface of silicon carbide

Monday, May 21, 2018

The gradual enrichment of the 6H-SiC (0001) surface with silicon atoms revealed two new reconstructions: a giant (12×12) and a (4×8) reconstruction. From STM images, an atomic model was constructed by introducing a new type of silicon in bridge between Si atoms of the SiC surface. These Si-bridge atoms also allowed to model two other reconstructions observed by other teams.

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(left) STM image of the giant (12×12) reconstruction obtained on the 6H-SiC (0001) surface after deposition of 1 monolayer of Si. (right) Atomic model of the (12×12) reconstruction optimized by molecular dynamics. The Si atoms of the (0001) SiC surface are in green, those of the first layer in yellow, and those in orange are at the top of the pyramids observed in STM image.

Hexagonal 6H (0001) silicon carbide is used in power microelectronics for its high bandgap energy (3 eV), and in the field of single-photon sources due to these surface states. In both cases, knowledge of surface reconstructions is essential to obtain the best components. Numerous studies based on the sublimation of an excess of silicon allow to discover different reconstructions, among which the (√3×√3)-R30° [1] and the (3×3) [2] have a known atomic structures, with 1/3 and 13/9 of silicon monolayers. Using a silicon enrichment procedure of the 6H-SiC (0001) surface, we discovered two other intermediate reconstructions: the giant (12×12) and the (4×8). From the position of the surface atoms observed in scanning tunneling microscopy, we have constructed atomic models by introducing a new type of silicon atoms. These so-called Si-bridge atoms are bonded to two silicon atoms of the terminal plane of the 6H-SiC(0001) crystal. They allow to make the link between reconstruction (√3×√3)-R30° and the following reconstructions such as (12×12) and (4×8). Atomic models were validated using molecular dynamics simulations with Tersoff potentials. These simulations showed the stability of the (12×12) up to 600 °C, and the (4×8) up to 900 °C, in good agreement with the experimental observations. In addition, these Si-bridge atoms are at the basis to model two other reconstructions observed experimentally by other teams: the (2√3×2√3)-R30° [3] and the (2√3×2√13) [4]. The analysis of silicon coverage rates and symmetry elements allowed us to generate a table with the six reconstructions known to date, and to present an unambiguous way of discerning them in situ by electron diffraction.

  1. A. Coati, M. Sauvage-Simkin, Y. Garreau, R. Pinchaux, T. Argunova, and K. Ad, Physical Review B 59, 12224 (1999), et autres citations incluses
  2. J. Schardt, J. Bernhardt, U. Starke, and K. Heinz, Phys- ical Review B 62, 10335 (2000), et autres citations incluses.
  3. F. Amy, P. Soukiassian, and C. Brylinski, Applied Physics Letters 85, 926 (2004).
  4. M. Naitoh, J. Takami, S. Nishigaki, and N. Toyama, Applied Physics Letters 75, 650 (1999) ;
    L. Li, Y. Hasegawa, T. Sakurai, and I. S. T. Tsong, Journal of Applied Physics 80, 2524 (1996).

Reference

Giant (12×12) and (4×8) reconstructions of the 6H-SiC(0001) surface obtained by progressive enrichment in Si atoms
David Martrou, Thomas Leoni, Florian Chaumeton, Fabien Castanié, Sébastien Gauthier, and Xavier Bouju
Phys. Rev. B 97, 081302(R) – Published 23 February 2018

Contact

David Martrou, CEMES (CNRS)
dmartrou at cemes.fr

 

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