Engineering strain relaxation of GeSn epilayers on Ge/Si(001) substrates

TL;DR

This study demonstrates how controlling the Ge buffer layer's thickness and growth recipe enables precise strain relaxation in GeSn epilayers on Ge/Si(001), facilitating the development of GeSn-based optoelectronic devices.

Contribution

It introduces a method to control strain relaxation in GeSn epilayers via buffer layer engineering, without causing Sn segregation, advancing epitaxial growth techniques.

Findings

Strain relaxation is mediated by threading dislocations in the Ge buffer layer.

Adjusting buffer layer parameters controls the degree of strain relaxation.

No additional dislocations are generated at the Ge-GeSn interface.

Abstract

A mechanism of controlling the degree of strain relaxation in GeSn epilayers, grown by molecular beam epitaxy on Ge/Si(001) substrates, is reported in this work. It is demonstrated that by suitably controlling the thickness and the growth recipe of the underlying Ge buffer layer, both fully-strained and highly-relaxed GeSn epilayers can be obtained, without significant Sn segregation. The strain relaxation of the GeSn epilayer is mediated by threading dislocations of the Ge buffer layer, propagating across the Ge-GeSn interface. Systematic estimation of the threading dislocation density in both the alloy epilayer and the Ge buffer layer, by the approach developed by Benediktovich et al. [A. Benediktovitch, A. Zhylik, T. Ulyanenkova, M. Myronov, A. Ulyanenkov (2015), J. Appl. Cryst. 48, 655-665] supports this observation, and also reveals that no additional dislocations are generated at the Ge-GeSn interface. Together with recently reported techniques to arrest dislocation propagation in GeSn epilayers, these results bode extremely well for realization of highly-relaxed GeSn epilayers, much coveted for development of GeSn-based emitters.