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Complex dielectric function of Si oxide as evaluated from photoemission measurements

We have studied the evaluation methodology of complex dielectric functions of the insulating films from photoemission measurements to accurately determine the energy band structure and electronic states for materials of interest. As a demonstration, SiO2 was selected for evaluation, because it is a typical insulator in metal-oxide-semiconductor devices. Measurement depth dependence of the energy loss signals for O 1s and Si 2p3/2 photoelectrons from the thermally-grown SiO2 have been systematically investigated to distinguish the surface contribution from the measured energy loss signals. After the removal of surface contribution from measured energy loss signals, the complex dielectric functions of thermally-grown SiO2 and CVD-SiO2 have been estimated. Obtained complex dielectric functions of SiO2 were also converted into optical constants and absorption coefficients, and the energy bandgap value of SiO2 was determined from a Tauc plot of the absorption coefficient.