Effects of Y doping on the structural stability and defect properties of cubic HfO2

Abstract

First-principles calculations have been performed to study the structural and electronic properties of pure and Y-doped cubic HfO2. It is found that Y doping in HfO2 would increase the stability of the cubic phase relative to the monoclinic phase by reducing the energy difference and the phase transition pressure. This result is consistent with the observed stabilization of the cubic phase of HfO2 by the addition of Y. The calculated formation energy of the VO–YHf complex defect in different charged states indicates that the single positively charged state (VO–YHf)+ is more stable than the neutral state (VO–YHf)0 and the double positively charged state (VO–YHf)++ in Y-doped cubic HfO2. Because the number of d-electrons of Y is less than that of Hf by one and substitutional Y for Hf introduces holes in the oxygen p-band, Y doping would make the highest occupied defect level induced by (VO–YHf)+ fall into the valence band rather than the energy gap, which explains the experimental observation that gap states related to oxygen vacancy defects become nondetectable in Y-doped HfO2 films.