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Motivated by a recent theoretical suggestion that doping electrons intovarious CaAl$_2$Si$_2$-type Zintl phase compounds may give rise to highthermoelectric performance, we explore the possibility of n-type (electroncarrier) doping of CaZn$_2X_2$ ($X$ = As, P) using first principlescalculation. We consider n-type doping of CaZn$_2X_2$ with the following twosituations: interstitial-site doping of alkaline earth metals $AE$ (= Mg, Ca,Sr, Ba) and group 3 elements $G3$ (= Sc, Y, La), and $G3$ substitutional dopingfor the Ca site. The evaluation of the formation energy of these defects invarious charged states reveals that the interstitial-site doping of $AE$ =Ca/Mg or $G3$ = Sc/Y, and $G3$ = La/Y substitutional doping for the Ca site arerelatively favorable among the possibilities considered. In particular, theformation energy of the La substitutional doping for the Ca site is the lowestamong the considered cases both for CaZn$_2X_2$ ($X$ = As, P) and is negative,which implies that La is expected to be substituted for the Ca site and provideelectron carriers spontaneously. We also find that for each doping caseconsidered, the formation energy of the defects is smaller for $X$ = As thanfor $X$ = P, which suggests that former is relatively easier to realize n-typedoping than the latter.

Possibility of n-type doping in CaAl$_2$Si$_2$-type Zintl phase compound CaZn$_2X_2$ ($X$ = As, P)