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

TL;DR

This paper demonstrates that group-3 elements like La, Y, and Sc are effective n-type dopants for Mg$_3$Sb$_2$, enabling higher electron concentrations than traditional chalcogen dopants, based on first-principles calculations and experimental validation.

Contribution

The study predicts and confirms that group-3 elements can serve as superior n-type dopants for Mg$_3$Sb$_2$, expanding doping options for thermoelectric applications.

Findings

Y is as effective as La as an n-type dopant.

Sc is slightly less effective than La and Y.

Doping with group-3 elements yields higher electron concentrations than chalcogens.

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 ($\sim10^{20}$ 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.