Surface electronic states in the fundamental gap of the clean and group III–V doped Si(110) surface

The surface electronic states in the fundamental gap of the clean Si(110) surface and the effect on them of Al, Pb and Sb adsorption were studied with the help of field effect kinetics and photovoltage experiments. The surface geometry and chemical composition were characterized by LEED and AES. The obtained results showed that the electron spectra of the clean Si(110) surface with 16 x 2 reconstruction have empty and filled bands. They were located near the midgap and separated from each other by an energy interval E gs 0.40 eV. Al, Pb and Sb adsorption on the Si(110)-16 x 2 phase at room temperature was followed by the formation of (1 X 1) LEED patterns with strong background for coverages < 2 ML. Drastic changes of the surface electron spectra under adsorption of these elements were revealed. Namely, the Si(110)/Al system contained shallow states only with an amazingly large gap E gs = 0.80 eV (!) between them. The surface barrier height corresponded to the Al-Si(110) contact potential difference. On the contrary, the Si(110)/Pb phase demonstrated one partially filled surface band with the top edge at 0.7 eV above the bulk valence band maximum. Finally, rather small changes were introduced in the surface electron spectra by Sb atoms. Some qualitative explanations of these effects were proposed concerning the links between atomic and electronic structures of the surface. In particular (1 x 1)Al RR and (1 x 1)Pb primitive unit cells could be suggested to explain the observed electron spectra changes.