Published in J. Vac. Sci. Technol. B 19, 1619 (2001).
Silicon on GaN(0001) and (0001) Surfaces
C. D. Lee,* R. M. Feenstra,* A. L. Rosa,** J. Neugebauer,** and J. E. Northrup***
*Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213
**Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg
4-6, D-14195 Berlin, Germany
***Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304
Surface reconstructions and adatom kinetics of silicon on GaN(0001)
and (0001) surfaces are studied by scanning tunneling
microscopy, electron diffraction and first-principles calculations. In
the low silicon coverage regime a 2×2 structure is observed, and
is interpreted in terms of a model consisting of a Ga adatom on a
monolayer of 3Ga + 1 Si and a SiGa atom in the third layer.
For high silicon coverage a 4×4 structure appears containing
disordered, partially 2×2 and "1×1" domains. After annealing above 300 C
the "1×1" region become dominant and the 4×4 region is seen only
near step edges. It is concluded that the silicon adatoms tend to
reside in subsurface sites on the Ga-polar surface. Surface
morphology in the presence of Si is smooth for the (0001) surface but
rough for the (0001) surface. This difference is attributed to
the presence of multiple Ga surface layers in the former case, which
enhance surface diffusivities.
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