Positioning of self-assembled Ge islands on stripe-patterned Si (001) substrates

TL;DR

This study investigates how self-assembled Ge islands grow on stripe-patterned Si (001) substrates, revealing their preferential locations influenced by temperature, surface morphology, and strain effects during molecular beam epitaxy.

Contribution

It provides new insights into the positioning mechanisms of Ge islands on patterned substrates, highlighting the roles of temperature, surface structure, and strain in their nucleation.

Findings

Ge islands prefer sidewalls at 650°C

Lower temperature (600°C) causes islands on top and sidewalls

Growth kinetics and strain influence island positioning

Abstract

Self-assembled Ge islands were grown on stripe-patterned Si (001) substrates by solid source molecular beam epitaxy. The surface morphology obtained by atomic force microscopy (AFM) and cross-sectional transmission electron microscopy images (TEM) shows that the Ge islands are preferentially grown at the sidewalls of pure Si stripes along [-110] direction at 650o C or along the trenches, whereas most of the Ge islands are formed on the top terrace when the patterned stripes are covered by a strained GeSi buffer layer. Reducing the growth temperature to 600oC results in a nucleation of Ge islands both on the top terrace and at the sidewall of pure Si stripes. A qualitative analysis, based on the growth kinetics, demonstrates that the step structure of the stripes, the external strain field and the local critical wetting layer thickness for the islands formation contribute to the preferential positioning of Ge islands on the stripes.