Surfactants: Perfect heteroepitaxy of Ge on Si(111)

In: Applied Physics A: Materials Science & Processing, Jg. 59 (1994) ; Nr. 5, S. 503-515
ISSN: 1432-0630
Zeitschriftenaufsatz / Fach: Physik
Fakultät für Physik » Experimentalphysik
The hetero growth of Ge on Si results in formation
of 3D clusters with an uncontrolled defect structure.
Introduction of a monolayer of a surfactant completely
changes the growth mode to a 2D-layer growth (Frankvan
der Merwe) with a continuous and smooth Ge film on
Si(ll 1). The surfactant is not incorporated but segregates
and floates on the growing Ge film. The saturation of the
dangling bonds of the semiconductor reduces the surface
free energy and drives the strong segregation. The effect on
the growth process is the selective change of activation energies
which are important for diffusion and the mobility
of the Ge. Up to a thickness of 8 MLs (MonoLayers) the
misfit-related strain of the pseudomorphic Ge film is relaxed
by formation of a micro rough surface. This allows a partial
relaxation of the Ge towards its bulk lattice constant which
would not be possible for a flat and continuous film. For
thicker Ge films the misfit of 4.2 % is relieved by a periodic
dislocation network, which is confined to the Si-Ge interface.
Ge-films thicker than 20 MLs are free of defects and
completely relaxed to the Ge bulk lattice constant: a model
system for perfect heteroepitaxial growth.