Atomic short-range order control of GeSn as a new degree of freedom for band engineering

TL;DR

This paper demonstrates that controlling chemical short-range order (SRO) in GeSn alloys during growth can significantly influence their bandgap, offering a new approach for band engineering in semiconductor devices.

Contribution

It quantifies SRO differences in GeSn grown by MBE and CVD and links SRO control to bandgap tuning for improved device performance.

Findings

MBE-grown GeSn shows stronger Sn-Sn SRO than CVD-grown samples.

SRO differences lead to a smaller bandgap in MBE-grown GeSn.

Surface termination and growth temperature influence SRO variations.

Abstract

Chemical short-range order (SRO) refers to preference or avoidance between neighboring atomic species, which significantly impacts the properties of advanced alloys. However, quantifying and further controlling SRO remains a major challenge, especially for semiconductor alloys. Inspired by theoretically predicted impact of SRO on the band structure of direct-bandgap GeSn for infrared photonics, we quantify and compare SRO in GeSn grown by molecular beam epitaxy (MBE) vs. chemical vapor deposition (CVD) using atom probe tomography. Remarkably, MBE-grown GeSn exhibits a stronger preference for Sn-Sn 1st nearest neighbors and an even smaller bandgap than CVD-grown samples with 2 at.% higher Sn composition. First-principles modeling confirms that the bandgap reduction originates from differences in SRO and further indicates that these SRO variations arise from different surface terminations and growth temperatures between MBE and CVD. These findings suggest that controlling SRO during GeSn growth offers a new degree of freedom for band engineering to achieve lattice-matched, high-quality Si-based electronic/photonic devices.