Instability of two-dimensional layers in the Stranski-Krastanov growth mode of Ge on Si(111)

Abstract

The surface morphology of Ge on Si(111) was studied using scanning reflection electron microscopy and energy dispersive x-ray spectroscopy. We found that in the Stranski-Krastanov growth mode, the nucleation of three-dimensional (3D) Ge islands at coverages above 2.3 bilayers (BL's) initiates disintegration of about 1 BL of a surface component of 2D Ge layers between the islands. Such a succession of structural transformation mainly determines the island size at coverages close to the 2D-3D transition. In the absence of islands, the 2D Ge layer at coverage between 1.5 and 2.3 BL remains thermally stable up to 500 \ifmmode^\circ\else\textdegree\fi{}C. Annealing at higher temperatures causes the transformation of the unstable surface component of the 2D layer into large (up to 3 \ensuremath{\mu}m in lateral dimension) flat islands. The surface morphology transforms through the generation of a supersaturated adlayer around the islands, which is similar to Ostwald ripening.