Defects controlled hole doping and multivalley transport in SnSe single crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Tin selenide (SnSe) is a highly promising thermoelectric material with exceptional performance.
• A complete understanding of its electronic structure and intrinsic hole-doping mechanisms remains elusive.
• This knowledge gap hinders the optimization of SnSe for advanced thermoelectric devices.

Purpose of the Study:

• To elucidate the anisotropic electronic structure of SnSe.
• To investigate the mechanism behind p-type (hole) doping in SnSe.
• To explore the relationship between electronic properties, defects, and thermoelectric performance.

Main Methods:

• Angle-resolved photoemission spectroscopy (ARPES) to probe electronic structure.
• Quantum transport measurements to investigate charge carrier behavior.
• Analysis of microdomain segregation and interfacial charge transfer.

Main Results:

• Revealed a unique, anisotropic, pudding-mould-shaped valence band with quasi-linear dispersion in SnSe.
• Demonstrated that p-type doping is controlled by SnSe2 microdomains and interfacial charge transfer, not intrinsic doping.
• Observed crystallographic axis-dependent quantum phenomena, including weak localisation and negative magnetoresistance, confirming the multivalley band structure.
• Quantum oscillations indicated a 3D Fermi surface and unusual interlayer coupling in p-SnSe, influenced by point dislocation defects.

Conclusions:

• The electronic structure of SnSe is highly anisotropic with unique band features.
• Extrinsic doping via SnSe2 segregation is the primary mechanism for p-type conductivity.
• Defect engineering, particularly addressing point dislocations, offers a promising strategy to enhance SnSe's thermoelectric properties.