Researcher reveals defects controlled hole doping and multivalley transport in SnSe single crystals


Thermoelectric materials are characterized by its Seebeck effect in converting heat into electricity and the Peltier effect in converting electricity into refrigeration in an efficient way, thereby becoming a promising type of environmentally-friendly energy source. The primary drawback with current thermoelectric materials is the fact that their thermoelectric figure of merit can hardly reach one.

However, researchers have reported an extraordinary thermoelectric conversion efficiency of ZT = 2.6 at 923 K in SnSe. Both Sn and Se are abundant on the earth, and the synthesis of their compounds is very convenient. Thus, SnSe is projected to have enormous promise. However, to date a comprehensive understanding of the electronic structure and most critically, the self-hole-doping mechanism in SnSe is still absent.

A research team led by Dr. ZHENG Yi in ZJU’s Department of Physics studied multivalley transport in SnSe single crystals, thereby providing solid evidence for synthesizing and ameliorating efficient thermoelectric materials. The work was done in collaboration with researchers from the Shanghai Institute of Microsystem and Information Technology and the Chinese Academy of Sciences (Shanghai).

They reported the highly anisotropic electronic structure of SnSe investigated by angle-resolved photoemission spectroscopy, in which a unique pudding-mould-shaped valence band with quasi-linear energy dispersion is revealed. They proved that p-type doping in SnSe is extrinsically controlled by local phase segregation of SnSe2 microdomains via interfacial charge transferring. The multivalley nature of the pudding-mould band is manifested in quantum transport by crystallographic axis-dependent weak localization and exotic non-saturating negative magnetoresistance. Strikingly, quantum oscillations also revealed 3D Fermi surface with unusual interlayer coupling strength in p-SnSe, in which individual monolayers were interwoven by peculiar point dislocation defects.

These results suggest that defect engineering may provide versatile routes in improving the thermoelectric performance of the SnSe family.




Department of Physics