Sb-surfactant mediated growth of Ge nanostructures

This paper reports the AFM and HREM study of the Sb surfactant mediated growth of Ge on Si(0 0 1). We show that very dense self-organised Ge dots of small lateral dimensions can be grown by using a sub-monolayer coverage of Sb on Si(0 0 1) in the transient growth regime between 2D nucleation and step flow. The dramatic Ge growth change induced by Sb is attributed to both kinetic and thermodynamic effects. Indeed, HREM observations evidence mainly two phenomena: the close-packing of ultra-small Ge islands indicating a lower surface diffusion in presence of Sb and a mono-modal island shape and size that strongly differs from the bimodal islands ‘huts’ and ‘domes’ commonly observed without Sb. Morphological and microstructural features of Ge islands formed with and without Sb are studied and the differences between facets and aspect ratio are exhibited. Moreover, at lower growth temperature (in the 2D nucleation regime, Tg⩽350 °C), a delay to 3D island nucleation is observed and defect free 2D flat layers can be grown up to thicknesses of ∼18 Å. At higher growth temperature, (in pure step flow at Tg∼750 °C) large, well separated ‘dome’ islands partially relaxed by dislocation nucleation on their edges are obtained. Such islands are very similar to those obtained without Sb coverage. The complete desorption of Sb on Ge rich surface at T>720 °C explains this result. This study which improves the understanding on the formation of ultra-small dense islands is very promising for the fabrication of quantum devices that require highly homogeneous islands of small lateral sizes and of MOSFET heterostructures with strained SiGe n-channel which require flat Ge rich layers with abrupt interfaces.