Electronic structure and thermoelectric properties of n- and p-type SnSe from first principles calculations

摘要

We present results of electronic band structure, Fermi surface and electrontransport properties calculations in orthorhombic $n$- and $p$-type SnSe,applying Korringa-Kohn-Rostoker method and Boltzmann transport approach. Theanalysis accounted for temperature effect on crystallographic parameters in$Pnma$ structure as well as the phase transition to $CmCm$ structure at$T_c\sim 807 $K. Remarkable modifications of conduction and valence bands werenotified upon varying crystallographic parameters within the structure before$T_c$, while the phase transition mostly leads to jump in the band gap value.The diagonal components of kinetic parameter tensors (velocity, effective mass)and resulting transport quantity tensors (electrical conductivity $\sigma$,thermopower $S$ and power factor PF) were computed in wide range of temperature($15-900 $K) and, hole ($p-$type) and electron ($n-$type) concentration($10^{17}-10^{21}$ cm$^{-3}$). SnSe is shown to have strong anisotropy of theelectron transport properties for both types of charge conductivity, asexpected for the layered structure. In general, $p$-type effective masses arelarger than $n$-type ones. Interestingly, $p$-type SnSe has stronglynon-parabolic dispersion relations, with the 'pudding-mold'-like shape of thehighest valence band. The analysis of $\sigma$, $S$ and PF tensors indicates,that the inter-layer electron transport is beneficial for thermoelectricperformance in $n$-type SnSe, while this direction is blocked in $p$-type SnSe,where in-plane transport is preferred. Our results predict, that $n$-type SnSeis potentially even better thermoelectric material than $p$-type one.Theoretical results are compared with single crystal $p$-SnSe measurements, andgood agreement is found.