High Pressure and Compositionally Directed Route to a Hexagonal GeSn Alloy Class

TL;DR

This study demonstrates that applying high pressure and temperature enables the formation of hexagonal GeSn alloys with tunable composition and symmetry, opening new pathways for optoelectronic materials.

Contribution

It introduces a novel high-pressure synthesis method to create hexagonal GeSn alloys with specific compositions and crystal symmetries, previously thought unachievable.

Findings

Hexagonal GeSn alloys can be synthesized at ambient conditions after high-pressure treatment.

Hexagonal symmetry is stable below 21 atom % Sn, cubic at or above this value.

The method enables tuning of material properties via composition and crystal structure.

Abstract

Despite their electronic dominance, cubic diamond structured Si and Ge, are optoelectronically deficient. Recent work indicates, however, that a volume-expanded hexagonal Ge modification can exhibit intensely sought, superior optoelectronic characteristics. If larger Sn could form a hexagonal solid solution with Ge, this would achieve this expansion. But this was not expected because Ge and Sn are unreactive at ambient conditions, Sn does not have an ambient hexagonal symmetry, and only cubic or tetragonal binary modifications could be prepared under any conditions including thin film processing. This state of affairs is categorically changed here by subjecting Ge and Sn to pressures of 9 and 10 GPa and temperatures up to 1500 K using large-volume press methods. Synchrotron angle-dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy reveal ambient pressure recovery of hexagonal 2H, 4H and 6H Ge-Sn solid solutions (P63/mmc). Formation of this new binary materials landscape is correlated with Sn uptake, with the hexagonal symmetry being accessible below 21 atom % Sn and the cubic diamond symmetry at or above this value. The findings form fertile routes to advanced materials, by in tandem creating reactivity with pressure and directing production of needed crystal symmetries with composition, as well as opportunity to tune properties based on crystal symmetry, composition, and stacking sequence for optoelectronic applications. PubMed Disclaimer