Surface Structures, Surfactants and Diffusion at Cubic and Wurtzite GaN
T. Zywietz, Jörg Neugebauer, M. Scheffler
Fritz-Haber-Institut der MPG
J. Northrup, Chris G. Van de Walle
Xerox Palo Alto Research Center
This article was received on Friday, June 26, 1998 and
accepted on Wednesday, September 23, 1998. Abstract
Clean
and As covered zinc-blende and wurtzite GaN surfaces have been investigated
employing density-functional theory calculations. For clean GaN surfaces our
calculations indicate the stability of several novel surface structures that
are very different from those found on traditional III-V semiconductors. Adding
impurities commonly present in significant concentrations during growth
strongly modifies surface reconstructions and energies. In particular, we find
that arsenic has a low solubility and significantly stabilizes the cubic GaN
(001) surface making it interesting as a potential surfactant. Finally, we have
studied the diffusion of Ga and N adatoms on both the equilibrium and
non-equilibrium surfaces. Our calculations reveal a very different diffusivity
for Ga and N adatoms: While Ga adatoms are very mobile at typical growth
temperatures, the diffusion of N adatoms is slower by several orders of
magnitude. These results give insight into the fundamental growth mechanisms
and allow conclusions concerning optimum growth conditions.
