Photoelectron spectroscopy as an in situ contact-less method for studies of MOS properties of ultrathin oxides on Si

tThe electric field across an ultrathin and uniform Si-oxide layer on a Si (1 1 1) surface and the positionsof the valence band edges at the Si-oxide/Si (1 1 1) interface have been probed by high-resolution syn-chrotron radiation induced photoemission spectroscopy, as an in situ contact-less method. Variation ofthe “gate bias” is achieved by depositing Sn nanoparticles on the ultrathin oxide surface. These nanopar-ticles, growing as isolated hemi-spherical islands, attract various quantities of negative charges from thesubstrate inducing a potential difference between the Sn islands/Si-oxide and Si-oxide/Si (1 1 1) interface.This method allows us to study and extract the locally varying electric field and changes in the positions ofthe edges of the valence bands by measuring the valence band spectra and the Si 2p and Sn 4d core-levelsat different Sn coverages. The ultrathin (0.8 nm thick) Si-oxide layer is grown in a simple and traceableself-limiting thermal process on a clean Si (1 1 1) surface. The oxide grown in this way creates flat bands.The properties of the system of Sn islands grown on this system are also determined. The induced electricfield in the oxide varies linearly with the amount of Sn deposited per area.