Impact of nitrogen on effective work function of metal/oxide stack: A first-principles study of the Pt/HfO₂ interface

Modulating the effective work function (Φ_eff) of metal electrodes is both crucial and challenging in metal-oxide-semiconductor transistors. The introduction of atomic dopants is shown to be an effective method to modify the interface Φ_eff. Here we apply the first principles calculations to systematically explore the impact of incorporation of the non-metallic ambient gas element N on the effective work function of a Pt/HfO₂ interface. We find that Φ_eff is very closely related to the doped atomic position and concentration of the incorporated N atoms. The incorporation is favored at the interface near HfO₂ side, and it can significantly increase the interface Φ_eff for the Pt/HfO₂ stack (making it more p-type). Also, the Φ_eff increases with the increase of doped N concentration due to the mitigation effect of doped N on interface dipole moment. Our findings will provide guidance in developing the environment annealing approach to modulation of Φ_eff of the metal/oxide stack.