Atomic and electronic structure of amorphous and crystalline hafnium oxide: X-ray photoelectron spectroscopy and density functional calculations

Abstract

The atomic structure of amorphous and crystalline hafnium oxide (HfO2) films was examined using x-ray diffractometry and Hf edge x-ray absorption spectroscopy. According to the x-ray photoelectron spectroscopy and band data calculated by the density functional method, we found that the valence band of HfO2 consists of three subbands separated by ionic gaps. The upper subband is formed by O 2p, Hf 4f, and Hf 5d states; the intermediate subband is formed by O 2s and Hf 4f states, whereas the lower narrow subband is mainly formed by Hf 5p states. The energy gap of amorphous HfO2 is 5.7eV as determined by electron energy loss spectroscopy. The band calculation results indicate the existence of light (0.3m0) and heavy (8.3m0) holes in the HfO2 film and the effective mass of electron lies in the interval of 0.7m0–2.0m0.