Tunable piezoelectric and ferroelectric responses of Al1-xScxN:The role of atomic arrangement

摘要

In this study,we present first-principles investigations of the atomic structure of Al_(1-x)Sc_(x)N and its influence on its piezoelectric and ferroelectric properties.The unbiased structure searching revealed that Al_(1-x)Sc_(x)N with phase separation feature,where Al N and Sc N form a layered structure with different symmetries,is more stable than the corresponding wurtzite structure.The piezoelectric response of Al_(1-x)Sc_(x)N is strongly dependent on the atomic arrangements;in particular,Al_(0.5)Sc_(0.5)N with a wurtzite structure exhibits a large positive e33of 4.79 C/m^(2),whereas Al_(0.5)Sc_(0.5)N with a phase separation structure exhibits a negative e33of-0.67 C/m^(2).Moreover,the ferroelectric switching of Al_(1-x)Sc_(x)N demonstrated two distinct pathways for the wurtzite and phase separation structures,and the spontaneous polarization thus calculated exhibits entirely different values.Accordingly,we demonstrated that Al_(1-x)Sc_(x)N with a phase separation structure exhibits a low polarization switching barrier of 0.15 e V/f.u.and a large spontaneous polarization of-0.77 C/m^(2);thus,it can serve as a novel Al_(1-x)Sc_(x)N-based ferroelectric material.As the dipoles in Al_(1-x)Sc_(x)N with a phase separation structure are localized in the AlN region,they are individually switchable at no domain wall energy cost and are stable against extrinsic effects.