Neutralizing Optical Defects in GeSn

TL;DR

This study demonstrates that doping Ge substrates can effectively suppress defect-related photoluminescence in GeSn layers, enabling clearer observation of intrinsic optical properties for potential optoelectronic applications.

Contribution

We introduce a doping strategy to reduce defect states in GeSn layers grown on Ge substrates, improving the clarity of photoluminescence signals.

Findings

Defect-related photoluminescence at 2400 nm is suppressed in doped Ge substrates.

Intrinsic GeSn emission at 2300 nm is observed without defect signals.

Doping fills localized defect trap states, enhancing optical quality.

Abstract

Reports of photoluminescence from GeSn grown on Ge substrates by molecular beam epitaxy have been limited. We find that one limiting factor to observing photoluminescence is due to localized defect states marked by photoluminescence at 2400 nm and originating from the Ge substrate and buffer layer. In this study, we report on an optical study utilizing doped Ge(001) substrates to effectively suppress defect-related photoluminescence in GeSn layers by filling localized defect trap states. For this experiment, a GeSn layer with Sn content up to 10.5% was grown on a doped Ge(001) substrate. Analysis of the physics of the photoluminescence spectrum collected from the GeSn thin film shows an emission at the expected wavelength of 2300 nm for 10.5% Sn content and the absence of the typically observed defect related signal at 2400 nm. This understanding is further confirmed using short pulse optical excitation of the GeSn grown on undoped Ge substrates.