First-principles studies of intrinsic point defects in magnesium silicide

Abstract

We have studied intrinsic point defects in magnesium silicide,Mg2Si, by density-functional theory. Evaluating the formation energiesof point defects, we show that n-type electric conductivity ofMg2Si originates from formations of positively charged Mg ions at interstitial sites, regardless ofthe chemical composition in crystal growth. Moreover, we have calculated the Borneffective charge tensors and the valence charge density distribution. They showMg2Si is an ionic crystalcomposed of Mg2+ and Si4− whichhave very different ionic radii, 0.6 Å and 2.1 Å, respectively. We have concluded that the unfavorable antisitedefect, MgSi, is due to the dissimilar ionic radii.