Effective $n$-type Doping of Mg${}_3$Sb${}_2$ with Group-3 Elements

Abstract

The recent discovery of high thermoelectric performance in Mg${}_3$Sb${}_2$ has been critically enabled by the success in $n$-type doping of this material, which is achieved under Mg-rich growth conditions, typically with chalcogens (Se, Te) as extrinsic dopants. Using first-principles defect calculations, we previously predicted that higher electron concentrations ($\sim 10^{20}$ cm${}^{-3}$) can be achieved in Mg${}_3$Sb${}_2$ by doping with La instead of Se or Te. Subsequent experiments showed that free electron concentration in La-doped Mg${}_3$Sb${}_{2-x}$Bi${}_x$ indeed exceeds those in the Te-doped material. Herein, we further investigate $n$-type doping of Mg${}_3$Sb${}_2$ and predict that, in addition to La, other group-3 elements (Sc, Y) are also effective as $n$-type dopants; Y is as good as La while Sc slightly less. Overall, we find that doping with any group-3 elements should lead to higher free electron concentrations than doping with chalcogens.