Photoemission studies of the surface electronic properties of L-CVD SnO2 ultra thin films

This work presents the results of systematic X-ray photoelectron spectroscopy (XPS) and photoemission yield spectroscopy (PYS) studies of the surface electronic properties of L-CVD SnO2 ultrathin films submitted to various technological treatments. The interface Fermi level position in the band gap EF - Ev has been determined from XPS analysis of the Sn3d5/2 binding energy position. Such value of the Fermi level position was in a good agreement with the value estimated from the offset of XPS valence band. The variation of interface Fermi level position, after the various technological treatments, has been compared to the change of work function obtained by PYS. Valence band XPS spectra and PYS spectra point to the presence of two different bands of filled electronic states of the L-CVD SnO2 thin films. The first one was localized in the upper part of valence band at the surface at about 6.0 eV below the Fermi level, whereas the second one was localized in the band gap at about 3.0 eV below the Fermi level. The changes of electronic properties of the space charge layer of L-CVD SnO2 ultrathin films submitted to different technological procedures were assigned to the observed variation of their surface chemistry, including stoichiometry/nonstoichiometry and to the presence of surface carbon contamination.