Microstructure-dependent band structure of HfO2 thin films

The effects of rapid thermal annealing on band structure of HfO2 have been investigated using combinational characterization techniques including X-ray diffraction, X-ray photoelectron spectroscopy and ultraviolet–visible spectrophotometer. The results show that the band structure of the thin film is strongly affected by crystalline structure. Different microstructures of HfO2 formed after annealing at a series of temperatures up to 1000 °C: amorphous below 450 °C, polycrystalline over 450 °C and good crystalline texture above 750 °C. The structure phase of polycrystalline thin films in theses samples remains basically unchanged. The HfO2 thin film shows a series of band structures corresponding to different microstructure properties. The further study shows that the band-gap energy increases after the polycrystallization of HfO2. Both valence band and conduction band shift downward, with a relatively smaller shift of the conduction band. A trap level forms below the conduction band after the polycrystallization of HfO2 thin films.