结合第一性原理和热力学计算对HfO_2晶体本征点缺陷的预测

Prediction of Native Point Defects in HfO_2 Crystals Using First Principles and Thermodynamic Calculations

基于第一性原理和热动力学方法模拟计算得到了不同温度和氧分压下Hf O2晶体本征点缺陷的形成能,并讨论了各种点缺陷的形成能随费米能级变化的规律.结果表明:当费米能级在价带顶附近时,随着温度和氧分压的变化,出现了不同的最稳定点缺陷(O0i、V2+O3和Hfi4+).当费米能级大于3.40 e V时,主要点缺陷是带-4价的Hf空位.该晶体除Hf空位在价带顶附近出现了奇数价态,其它的点缺陷都只显现偶数价态,这表明该晶体的点缺陷具有典型的negative-U特性.本文还计算得到了该晶体可能存在的最稳定点缺陷在温度、氧分压和费米能级三维空间的分布,这为分析该晶体在不同条件下可能出现的点缺陷类型提供清晰的图像,为调控晶体点缺陷的形成提供参考.

Based on first principles and thermodynamics the intrinsic point defect formation energy was calculated at different temperatures and oxygen partial pressures in Hf O2 crystals. The stability of all kinds of point defects as well as the formation of charged point defects and their sensitivity to the Fermi energy was analyzed. We also discuss rules that govern the formation of various point defects that vary with Fermi level.The results show that with a change in temperature and oxygen partial pressure the most stable point defects are obtained（Oi^0, VO3^2＋and Hfi^4＋） when the Fermi level is close to the valence band. The main point defect was the Hf vacancy at a-4 charge when the Fermi level was higher than 3.40 e V. Apart from the Hf vacancy almost no other point defect had an odd charge and they showed negative-U behavior. Using the most stable intrinsic defect as a function of the Fermi level, the oxygen partial pressure and the temperature were determined using three-dimensional defect formation enthalpy diagrams. This diagram provides information that allows for the control of point defects in the crystal.