Segregation of oxygen vacancy at metal-HfO2 interfaces

We perform first-principles calculations on metal-HfO2 interfaces in the presence of oxygen vacancies. Pt, Al, Ti, and Ag are considered as electrodes. It is found that oxygen vacancies are strongly attracted to the interface with binding energies of up to several eVs. In addition, the vacancy affinity of interfaces is proportional to the work function of metals, which is understood by the transition level of the vacancy and metal-Hf bonding. Interfacial segregation of vacancies significantly affects effective work functions of p metals. Our results are consistent with flatband shifts in p-type field effect transistors employing high-k dielectrics and metal gates.