Density functional calculations of the Schottky barrier height and effective work function in Ni/oxide interfaces

In high-k/metal gate stacks of complementary metal-oxide semiconductor devices, it is important to control the effective work functions of metals such that they should match to the doping levels of poly-Si gates. However, it is known that metal work functions are strongly affected by interface dipoles and defects. In this work, we perform first-principles density-functional calculations to study the Schottky barrier heights and the effective metal work functions in Ni/SiO$_2$ and Ni/HfO$_2$ interface structures. We use the advanced approaches such as hybrid density functional and quasi-particle \textit{GW} calculations for the exchange-correlation potential and discuss the limitations of GGA calculations. We also examine the effects of O-vacancy defects introduced at the interface on the Schottky barrier height and the effective work function. We find that, in the Ni/HfO$_2$ interface, the $p$-type Schottky barrier height tends to increase with increasing of the defect density due to the charge transfer at the interface, whereas it is little affected in the Ni/SiO$_2$ interface.