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

Area of Science:

• Materials Science
• Solid-State Physics
• Optoelectronics

Background:

• Cubic silicon (Si) and germanium (Ge) are optoelectronically limited.
• Hexagonal Ge modifications show promise for superior optoelectronic characteristics.
• Forming hexagonal Ge-Sn alloys was previously considered unachievable due to Sn's properties and Ge-Sn's low reactivity.

Purpose of the Study:

• To investigate the possibility of forming hexagonal Ge-Sn solid solutions.
• To explore the synthesis of Ge-Sn alloys with tunable optoelectronic properties.
• To overcome the challenges of Ge-Sn reactivity and Sn's crystallographic limitations.

Main Methods:

• High-pressure synthesis using large-volume presses (9-10 GPa, up to 1500 K).
• Characterization via Synchrotron angle-dispersive X-ray diffraction.
• Analysis using precession electron diffraction and electron microscopy.

Main Results:

• Successful synthesis and ambient pressure recovery of hexagonal 2H, 4H, and 6H Ge-Sn solid solutions.
• Hexagonal symmetry observed below 21 atom % Sn; cubic diamond symmetry at or above this threshold.
• Demonstrated correlation between Sn content and resulting crystal symmetry.

Conclusions:

• High pressure enables Ge-Sn reactivity and formation of novel hexagonal solid solutions.
• Composition dictates crystal symmetry, offering a route to tune optoelectronic properties.
• This work opens avenues for advanced optoelectronic materials based on Ge-Sn alloys.