Hole-doping reduces the coercive field in ferroelectric hafnia

Abstract

Ferroelectric hafnia (HfO2) holds promise for next-generation memory and logic applications because of its CMOS compatibility. However, the high coercive field required for polarization switching in HfO2 remains a critical challenge for efficient device operations. Using first-principles calculations and phenomenological modeling, we predict that hole doping can reduce the coercive field from 8 MV/cm in undoped hafnia to 6 MV/cm in hafnia doped with 0.2 holes per formula unit (f.u.). In the absence of doping, the reversal of polarization of the Pca21 phase is preferred through the non-polar, tetragonal P42/nmc phase. This switching pathway involves the coupling of three hard distortion modes that render undoped hafnia as an improper ferroelectric. The overall energy barrier through this pathway remains unchanged (80 meV/f.u.) upon hole doping. However, the introduction of holes hardens the polar distortion mode that connects the polar Pca21 phase to the non polar, orthorhombic Pbcm phase, and reduces the energy barrier from 180 meV/f.u. in undoped hafnia to 80 meV/f.u. at 0.2 holes/f.u.. The activation of the latter switching pathway through the Pbcm phase can lead to a reversal in the polarization direction. Overall, hole doping makes the switching pathway through the Pbcm phase competitive, and renders hafnia as a proper ferroelectric with a lower coercive field.