Decoupling the effects of composition and strain on the vibrational modes of GeSn

TL;DR

This study uses Raman spectroscopy to analyze how composition and strain independently affect vibrational modes in GeSn semiconductors, providing a method to accurately determine Sn content and strain.

Contribution

It introduces an empirical Raman-based method to decouple and quantify the effects of composition and strain in GeSn layers, enhancing material characterization.

Findings

Vibrational modes shift linearly with Sn content and strain.

Broadened and asymmetric peaks correlate with composition and strain.

Empirical method accurately quantifies Sn content and lattice strain.

Abstract

We report on the behavior of Ge-Ge, Ge-Sn, Sn-Sn like and disorder-activated vibrational modes in GeSn semiconductors investigated using Raman scattering spectroscopy. By using an excitation wavelength close to E1 gap, all modes are clearly resolved and their evolution as a function of strain and Sn content is established. In order to decouple the individual contribution of content and strain, the analysis was conducted on series of pseudomorphic and relaxed epitaxial layers with a Sn content in the 5-17at.% range. All vibrational modes were found to display the same qualitative behavior as a function of content and strain, viz. a linear downshift as the Sn content increases or the compressive strain relaxes. Simultaneously, Ge-Sn and Ge-Ge peaks broaden, and the latter becomes increasingly asymmetric. This asymmetry, coupled with the peak position, is exploited in an empirical method to accurately quantify the Sn composition and lattice strain from Raman spectra.