4-Monolayer-Height Layer-by-Layer Growth and Increase of the Critical Thickness of Ge Heteroepitaxy on Boron-Preadsorbed Si(111) Surface

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Abstract
Heteroepitaxy of Ge was performed onto clean Si(111)7×7 and 1-monolayer (ML) boron-preadsorbed Si(111)√ 3×√ 3R30°–B surfaces held at 500° 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.