Near-edge optical absorption behavior of sputter deposited hafnium dioxide

The absorption behavior at the onset of the ultraviolet optical edge of sputter deposited hafnium dioxide is reported. X-ray diffraction showed that films grown at room temperature on fused silica were nanocrystalline monoclinic, and that after air annealing at 1273 K for 24 h, they were well-crystallized monoclinic with a strong (11-1) texture. Spectrophotometry was used to measure transmission and reflection in the 190-1100 nm wavelength range. The absorption coefficient, alpha(E), as a function of energy, E, was determined from spectrophotometric data. Two persistent features were identified. Feature I is the rapid rise in alpha(E) above 6.24 eV that is unchanged upon annealing. A linear alpha(E)(1/2) vs E dependence associates this feature with indirect interband transitions. Feature II initiates at similar to 5.65 eV and saturates at 5.94 eV. It appears as a low energy shoulder on the absorption edge of the as-grown films and develops into a discrete and more intense band in the annealed films, in which the coordination of Hf with seven O is satisfied. Its annealing behavior explicitly shows that feature II is not caused by an O defect, but is intrinsic to monoclinic HfO2. (c) 2007 American Institute of Physics.