Alkali metals adsorbed on III-V(110) surfaces have been studied for decades due to the interest in the mechanisms of the Schottky barrier formation and the Fermi level pining at metal-semiconductor interfaces. These systems are thought to be the ideal playground for the investigations of metal-semiconductor interface due to the following reasons. (i) From a theoretical point of view, this system provides a simplified model, because only one valence electron at the outer most shell should be considered. (ii) III-V(110) surfaces, especially GaAs(110), are the well-known semiconductor surfaces experimentally and theoretically. (iii) Since the relaxation of the topmost atoms induce the movement of the surface states of the III-V(110) out of the bulk bandgap, it has advantage to investigate the metal-induced gap states. Photoemission spectroscopy experiment showed that alkali atom adsorption induced a surface state within the gap [1] and theoretical work also predicted that the alkali atoms forming asymmetric chain structure induced surface state above the valence edge [2]. However, there have been no experimental results to correlate the adsorption structure of alkali atoms with the electronic properties.
In this work, we performed STM/STS measurements on the K/GaAs(110) surfaces to investigate the structural and electronic properties. Obtained differential tunneling conductance at the K adsorption site showed the characteristic peak at the negative sample bias that was related to the K induced surface state. Taking into account the theoretical work, the surface state should be located above the valence edge of GaAs. However, the peak was observed at the lower energy than the valence edge. The peak shift will be considered from the local band bending at the K site due to the positive charge.
[1] K. O. Magnusson et al. Phys. Rev. B 40 (1989) 7814.
[2] A. Calzolari et al., Surf. Sci. 491, (2001) 265.
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