Electronic structure analysis of Zr silicate and Hf silicate films by using spatially resolved valence electron energy-loss spectroscopy

Abstract

Electronic structures near the band gaps of Zr silicate and Hf silicate thin films were investigated experimentally and theoretically. We show that the electronic structure of Zr silicate can be reproduced by a superposition of the electronic structures of ZrO2 and SiO2. Similarly, the electronic structure of Hf silicate can be reproduced by a superposition of the electronic structures of HfO2 and SiO2. This indicates that, in these silicates, the lowest conduction band states are composed mostly of d states of Zr or Hf, and the valence band states mostly of O 2p states. The similarity of the electronic structures of these silicates can be attributed to the similarity of the chemical natures of Zr and Hf atoms. Consequently, when these silicate films are used as gate dielectrics in metal–oxide–semiconductor transistors, the gate leakage current could be strongly affected by d states of Zr or Hf.