Electron energy-loss spectroscopy in a scanning transmission electron microscope (STEM-EELS) and ab initio electronic structure calculations were used to analyze how the chemical composition of a Hf{sub}xSi{sub}(1-x)O{sub}2 film affects the electronic structure near the bandgap. We first show that the bandgap of Hf-rich Hf{sub}xSi{sub}(1-x)O{sub}2 (x ≥ 0.5) is identical to that of HfO{sub}2 because the energy gap between O 2p and Hf 5d states determines their bandgaps, and because Si-derived states barely affect the energy gap between O 2p and Hf 5d states in Hf{sub}xSi{sub}(1-x)O{sub}2. Second, we show that incorporation of N into a Hf{sub}xSi{sub}(1-x)O{sub}2 film changes the valence band structure and reduces the bandgap. Finally, we show that these results can explain the previously reported chemical composition dependency of the dielectric constant of Hf{sub}xSi{sub}(1-x)O{sub}2 and the N concentration dependency of the dielectric constant of N-incorporated Hf{sub}xSi{sub}(1-x)O{sub}2.
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