Thermoelectric Property of SnSe Films on Glass Substrate: Influence of Columnar Grain Boundary on Carrier Scattering

Thermoelectric SnSe exhibits a very high figure of merit, and the a-axis orientation is needed because a high thermoelectric property is obtained along the bc-plane. Here, in spite of the amorphous nature of glass, a-axis-oriented SnSe films were fabricated using pulsed laser deposition on a glass substrate, which is more practical than single-crystal oxide substrates. Transmission electron microscopy indicated that a-axis-oriented SnSe films with a columnar grain structure grew on amorphous SiO2. The electrical conductivity and the Seebeck coefficient at room temperature showed almost the same trend with respect to the hole concentration in both the SnSe/glass and SnSe/single-crystal-substrate films. The electrical conductivity increased with increasing temperature more slowly in SnSe/glass films than in SnSe/single-crystal-substrate films. This indicates that the grain boundary contribution to carrier scattering is significant at high temperatures, while the grain boundary contribution is as strong as the orthorhombic domain boundary contribution at room temperature. In spite of the grain boundary effect, the power factor in SnSe/glass was as high as that for single-crystal SnSe at high temperatures. Considering the grain boundary effect on electrical conductivity, the structure and process of SnSe films on amorphous substrates should be designed.