First-Principles Study on Electronic Structure of Gd-Doped HfO2 High k Gate Dielectrics

The 6.25 mol% Gd-doped HfO2 high k gate dielectrics were investigated by first-principles calculations, based on the density functional theory, using the code of Vienna ab-initio simulation package (VASP). Equilibrium crystal structures and electronic structures were characterized. The simulation cell consists of a cubic structure with 96 atoms (32 Hf atoms and 64 O atoms), two Gd substituted atoms for Hf (Gd-Hf). To satisfy the charge neutrality of the system, we setup a complex defect [(Gd-Hf)(2)V-O](0) by removing an O atom near the two Gd atoms. There are four sevenfold coordination Hf atoms in the optimized structure of the supercell with 96 atomic sites. This is beneficial to the stabilization of the cubic phase with high dielectric constant and the decrease of oxygen vacancies. Meanwhile, this complex defect increases the band gap of Gd-doped HfO2. In addition, the charged defect [(Gd-Hf)(2)VO](-) was also explored. The d-d coupling of Hf 5d and Gd 5d antibond state electrons through an O atom (Gd-O-Hf) is confirmed theoretically, which is considered as the main reason for the broadening of the band gap. The calculation results are in accord with experimental data.