4-Monolayer-height layer-by-layer growth and increase of the critical thickness of Ge heteroepitaxy on boron-preadsorbed Si(111) surface

Heteroepitaxy of Ge was performed onto clean Si(111)7 x 7 and 1-monolayer (ML) boron-preadsorbed Si(111)root 3 x root 3R30 degrees-B surfaces held at 500 degrees C. Both cases of growth showed the Stranski-Krastanov (SK) growth mode. On the clean surface, layer-by-layer growth by 2-ML-height two-dimensional (2D) islands lasted for up to 6 ML of Ge growth, and then relaxed 3D islands began to be formed. On the boron-preadsorbed surface, however, critical thickness for the formation of 3D islands increased to 8 ML due to suppression of Ge surface migration by surface-segregated boron atoms. It was confirmed by atomic force microscopy (AFM) that the height of 2D islands appearing in the layer-by-layer growth process changed from the normal 2 ML to 4 ML on the boron-preadsorbed surface.