Systematic studies of the effects of group-Ⅲ dopants (La, Y, Al, and Gd) in Hf_(0.5)Zr_(0.5)O_2 ferroelectrics by ab initio simulations

摘要

La-doped Hf_(0.5)Zr_(0.5)O_2 (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.