G.M. Guichar

Effects of low oxygen exposures on the electronic surface properties of GaAs (110)

Abstract The first stages of oxygen adsorption, for exposures from 0.1 to 10 4 L on cleaved surfaces of n and p-type GaAs samples, are investigated by Photoemission Yield Spectroscopy. For any doping, the evolution of the density of states in the gap with oxygen exposures depends on the quality of the cleave. It is shown that, for good cleaves of the most highly doped n-type samples, an oxygen-induced band appears in the gap at exposures as low as 1 L. This effect is discussed, assuming changes in the initial structure of the clean surface.

Structure dependent oxidation of clean Si(111) surfaces

Abstract The initial process of oxygen adsorption is investigated by high resolution photoemission yield spectroscopy on (2 × 1) and (7 × 7)Si(111) surfaces. The corresponding changes in work function, ionization energy and surface state distribution, within and close to the gap, depend strongly on the initial structure. It is shown for the first time that, after completion of a “monolayer” of oxygen, the dangling bond states completely disappear on the (7 × 7) structure while a few percents remain unaffected on the (2 × 1).

Photoemission yield spectroscopy of electronic surface states on germanium (111) surfaces

Abstract The electronic surface states of cleaved and annealed Ge(111) surfaces have been investigated by photoemission yield spectroscopy and contact potential measurements on a set of differently doped samples. On the 2 × 1 cleaved surface, a surface state band centered about 0.7 eV below the valence band maximum is found. The variations of the work function with the doping level show that an empty surface state band exists above the Fermi level. After annealing at temperatures of the order of 350°C, this surface exhibits a 2 × 8 superstructure. A new surface state band is then found closer to the valence band maximum. This variation of the surface state distribution is correlated to a change in the surface potential. The variation of the electronic characteristics upon oxygen adsorption are also reported and an evaluation of the sticking coefficient is made for both structures.

Semiconductor surface state spectroscopy

Abstract We present here a review of optical spectroscopic methods applied to semiconductor surface states. Some results on Si, Ge, III–V compounds obtained by ultraviolet photoemission spectroscopy and photoemission yield spectroscopy are emphasized and compared with theoretical calculations. It is shown that the confrontation of theory and experiments can give now a rather good understanding of the electronic properties of clean surfaces.

Electronic surface properties of cleaved GaP(110)

Abstract Electronic surface properties of UHV cleaved GaP (110) are investigated by contact potential difference measurements and photoemission yield spectroscopy. The p-type samples show practically no band bending; n-type GaP exhibits surface Fermi level stabilization about 1.65 eV above the valence band maximum. Two surface state bands are found in the gap. The importance of the first one, located near the valence band edge, depends on the cleavage. The other one is found in the upper part of the gap. An evaluation of the corresponding density of states shows it may correspond to the tail of an intrinsic surface band, mostly empty, the maximum of which would be closer to the conduction band. By comparing with results on other III–V compounds, it is suggested that a surface relaxation smaller for GaP than for GaAs may explain their different electronic properties.