Characterization of surface electric field in β-FeSi2 by Franz–Keldysh oscillations

Abstract

The surface electric field (F) of β-FeSi2 has been investigated by Franz–Keldysh oscillations (FKOs) observed in photoreflectance spectra. The FKO signals were observed in an undoped β-FeSi2 epitaxial layer (3 nm) grown on p+-type β-FeSi2 layers (UP+ structure) by molecular beam epitaxy. The surface electric field obtained from the FKO at 11 K was F = 220 kV/cm. The surface electric field was almost independent of the excitation light power and temperature, showing that the surface electric field was not affected by the surface photovoltage effect. In the dependence of F on the thickness of the undoped layer (d), F was nearly constant at d = 2–56 nm. The result showed that the surface electric field of β-FeSi2 was applied to a thin region (<2 nm) at the surface.