The electrical properties of Na overlayers on the clean, cleaved GaAs(110) surface

The electrical properties of moderately doped Na/n-GaAs(110) Schottky diodes, fabricated on the clean, cleaved GaAs(110) surface under ultra-high vacuum conditions, have been studied in situ. The Schottky barrier height extracted from the current-voltage characteristics of several diodes lies in the range 0.69-0.72 V. The barrier height obtained from the conventional capacitance-voltage technique (ignoring the image force correction of about 0.03 V) lies slightly higher (0.76-0.82 V). Moreover, the Ga and As 3d core-level emission, measured using synchrotron-radiation-excited soft-X-ray photo-emission spectroscopy, exhibit metal-induced shifts associated with semiconductor band bending. These measurements suggest that, like many other metals, Na pins the GaAs Fermi level close to mid-gap despite its extremely low work function and low electronegativity.