Systematic studies of the effects of group-III dopants (La, Y, Al, and Gd) in Hf0.5Zr0.5O2 ferroelectrics by ab initio simulations

Abstract

La-doped Hf0.5Zr0.5O2 (HZO) ferroelectrics have demonstrated great potential to solve the endurance challenge of hafnia-based ferroelectric memory. In this work, we systematically studied the doping effects of La in HZO by ab initio simulations and theoretically compared it with three other commonly used group-III dopants (Al, Y, and Gd). The physical mechanisms behind superior endurance are thoroughly analyzed based on the calculation results regarding phase stability, oxygen vacancy formation energy, migration barrier, and electronic structures. It has been discovered that among the four dopant candidates, La has the strongest stabilization effect of the ferroelectric phase in HZO. Also, under stoichiometric doping conditions, La and other group-III dopants were observed to increase the oxygen vacancy formation energy and make HZO less susceptible to dielectric breakdown. Finally, La, Al, or Y dopants replacing Hf or Zr can getter migrating oxygen vacancies and passivate the associated defect states in the bandgap. Based on these observations, guidelines were proposed for designing the doping method and concentrations to achieve the best endurance.