The effect of oxygen adsorption on the electronic properties of the polar GaAs(111) surface after thermal cleaning in ultrahigh vacuum

The influence of oxygen adsorption on the electronic properties of clean, polar n-type GaAs(111)As surfaces prepared by prolonged ultrahigh vacuum heating at 770 K have been investigated by means of photoemission yield spectroscopy combined with Auger electron spectroscopy control. For the clean surface the evaluation of arsenic content strongly depends on the theoretical models used whereas the work function φ and absolute band bending eVs were 4.05±0.03 eV and -0.21±0.07 eV respectively. Moreover, two stable filled electronic surface state bands localized in the band gap tailing up to Fermi level E_F and above the top of the valence band at the surface were observed. After exposure of this surface to 10³ L of oxygen the work function φ and absolute band bending eVs increased by 0.13 eV and the filled surface state band close to the Fermi level E_F drastically decreased in amplitude. For oxygen exposures of 10⁴ L and 10⁵ L the above parameters increased only by 0.09 eV and 0.04 eV respectively whereas the filled surface state band above the top of the valence band at the surface was stable.