Unpinning of the Fermi level at (111)A clean surfaces of epitaxially grown n-type In0.53Ga0.47As

Low-temperature scanning tunneling spectroscopy under ultrahigh vacuum was employed to investigate the (111)A clean surface of n-type In0.53Ga0.47As, grown by molecular beam epitaxy on lattice-matched InP substrates. It was found that the surface Fermi level is located in the conduction band, close to the bulk Fermi level, and can be controlled by varying the dopant concentration in the bulk. This observation was confirmed by determining the dispersion relation of electron standing waves resulting from scattering interferences. Such an unpinning of the surface Fermi level strongly contrasts with the pinning phenomenon observed at the (001) clean surface.