On the ferroelectricity in wurtzite materials

Abstract

As the dielectric film thickness shrinks to ∼10 nm, some traditional wurtzite (WZ) piezoelectric materials demonstrate ferroelectricity through element doping. Among them, Sc doped AlN and Mg doped ZnO are well-known examples. While it is widely acknowledged that the dopant atoms effectively reduce the coercive field, enabling ferroelectric polarization switching, the material genome of these WZ ferroelectrics is still less understood. In this work, we analyze the features of WZ ferroelectrics, ascribing them as five-coordination (5C) ferroelectrics, which may be compared with those of 6C ferroelectrics (perovskite-type) and 7C ferroelectrics (hafnia-like). In particular, the exact reason for their adoption of the hexagonal WZ structure instead of the zinc blende structure is studied. Attention is paid to the degree of ionicity in promoting the hexagonal arrangement, and the phenomenon of layer distance compression is discovered and explained in WZ ferroelectrics. The role of element doping in coercive field reduction is understood within this context.