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

Abstract The electric field across an ultrathin and uniform Si-oxide layer on a Si (1 1 1) surface and the positions of the valence band edges at the Si-oxide/Si (1 1 1) interface have been probed by high-resolution synchrotron radiation induced photoemission spectroscopy, as an in situ contact-less method. Variation of the “gate bias” is achieved by depositing Sn nanoparticles on the ultrathin oxide surface. These nanoparticles, growing as isolated hemi-spherical islands, attract various quantities of negative charges from the substrate 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 of the edges of the valence bands by measuring the valence band spectra and the Si 2p and Sn 4d core-levels at different Sn coverages. The ultrathin (0.8 nm thick) Si-oxide layer is grown in a simple and traceable self-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 electric field in the oxide varies linearly with the amount of Sn deposited per area.