First-principles study on thermodynamic stability and electronic structures of the ferroelectric binary HfO2 and ZrO2 (001) polar surfaces

Abstract

Using the reliable first-principles thermodynamic method, the relative stability and electronic states of ferroelectric binary HfO₂ and ZrO₂ (001) polar surfaces with different stoichiometry are comprehensively investigated. The results predict that the thermodynamically preferred surface termination is the O₄-(Hf or Zr)₂- for both the HfO₂/ZrO₂ positively (Z+) and negatively (Z−) polar surfaces under most chemical environmental conditions, which is in same oxygen content as each other, providing convenient and feasible strategy for designing high-performance devices based on HfO₂ (or ZrO₂) ferroelectric dielectric. In addition, the surface morphology, atomic geometries, and electronic states of HfO₂ and ZrO₂ (001) polar surfaces show evident dependence on polarization direction. There exists significant difference in the polar surface atomic relaxations, electronic band structures, work functions, and compensating charges between the Z+ and Z− polar surfaces of ferroelectric HfO₂/ZrO₂. In other words, the surface properties of HfO₂/ZrO₂ Z± polar surfaces are strongly revised by the partially occupied surface electronic states induced by the polar surface terminations. Our study is of great significance for the design and development of the next generation of high-performance and energy-efficient field-effect nanodevices based on HfO₂ (or ZrO₂) ferroelectric dielectric.