Charge-compensated co-doping stabilizes robust hafnium oxide ferroelectricity

Abstract

Doping with various cations is considered to be a key method for inducing ferroelectricity in HfO₂. However, previous studies often neglected the role of carriers introduced by heterovalent dopants. Here, using first-principles calculations, we show that carriers profoundly affect the stability of polar phases and advocate that carriers should be considered as a fundamental framework for understanding the origin of ferroelectricity in doped HfO₂. Although doping with p-type elements that introduce holes can stabilize the polar phase, it is not sufficient to make them the ground state phase. However, when they are co-doped with an n-type V element, they not only stabilize the polar phase to the ground state, but also achieve charge neutrality through electron compensation. This is due to the formation of deep energy levels (electron–hole recombination centers) by V doping, similar to oxygen vacancies. Unlike oxygen vacancy compensation, which favors the formation of tetragonal phases, co-doping is more favorable for the formation of polar phases and the absence of structural defects. Our results contribute to the understanding of the origin of HfO₂ ferroelectricity and provide a potential method for the preparation of HfO₂-based films with excellent ferroelectric properties.