A STUDY OF THE LAF3/SI(111) INTERFACE USING UPS AND XPS

LaF3 layers ranging in thickness from submonolayer to several monolayers were deposited onto room temperature Si(111)-7 × 7 clean surfaces, and subsequently annealed at temperatures from 400°C to 750°C to promote ordering. The overlayers and the detailed interface reactions were probed with high resolution XPS in our home laboratory, and by soft XPS using the synchrotron source SRS at Daresbury laboratory, both systems used in conjunction with LEED. The experiments show that though high quality epitaxial layers may be grown, the interfaces, nevertheless, are complex with a preference for the formation of La-Si bonds. Upon further annealing to temperatures in the range 800°C to 1200°C, strong chemical reactions were observed leading to the total desorption of fluorine and the formation of lanthanum silicide. This was confirmed by detailed studies of the interactions of La metal with Si under similar annealing conditions, and by LEED. Fluorine could also be removed from the epilayers by exposure to high intensity synchrotron radiation, leading to the possibility of exploitation in the fabrication of 3D device structures. Finally a value of 7.9 ± 0.1 eV was measured for the valence band offset of the LaF3/Si(111)-7 × 7 system, compared with 7.75 eV predicted by the Anderson model when used in conjunction with Nethercote's equation for the photoelectric threshold. © 1990 IOP Publishing Ltd.