Interface states in the Si band-gap obtained from XPS measurements under biases

Measurements of X-ray photoelectron spectra were performed for [similar to 3 nm Pt/2.5-3.6 nm SiO2/n-Si(100)] MOS devices under biases between the Pt layer and the Si substrate. The Si 2p peaks due to the Si substrate and the oxide layer are both shifted by biasing, the magnitude of the shift of the former peak being much larger than that of the latter. The shifts are well correlated to each other, and are attributed to a change in the potential drop across the oxide layer caused by charges in interface states. Using the method developed by us, the interface states are found to have discrete energy levels with energies depending on the formation method of the silicon oxide layers, and are attributed to Si dangling bonds in various environments.