XPS analysis and valence band structure of a low-dimensional SiO₂/Si system after Si⁺ ion implantation

A X-ray photoelectron spectroscopy (XPS) of valence band (VB) and core levels are performed for a SiO₂/p-Si heterostructure containing a thin oxide layer of d = 20 nm thickness and implanted by Siþ ions. With an implantation energy of 12 keV the maximum density of the implanted Si⁺ profile is located close to the SiO₂–Si interface at a depth of 18 nm, but a piling-up of Si is also found immediately beneath the surface up to 2 nm, i.e., within the escape depth of XPS electrons. Thus we may expect a partial phase separation associated with Si aggregation and nanocluster formation imbedded in a nonstoichiometric SiO_x matrix. By means of XPS and in comparison to X-ray emission spectroscopy (XES) the related changes of the VB structure are investigated.