Oxygen and fluorine adsorption and their coadsorption on the (111) unreconstructed surface of semiconductors InAs and GaAs were studied using the projector augmented-wave method with the generalized gradient approximation for the exchange−correlation functional and hybrid functional approach. The energetically preferable adsorbate sites on the surface were determined. It is shown that fluorine adsorption above surface cations on the A III B V (111)A-(1 × 1) unreconstructed surface leads to a removal of the surface state formed by cation p z -orbitals and to an unpinning of the Fermi level, whereas oxygen adsorption induces additional surface states in the band gap. The influence of fluorine and oxygen coadsorption and also fluorine concentration on the surface states in the band gap is discussed. It is shown that oxygen-induced surface states are completely or partially removed from the band gap by fluorine coadsorption if it forms bonds with cation surface atoms involved in an interaction with oxygen. The increase of fluorine concentration leads to considerable changes of the near-surface-layer structure due to the penetration of both electronegative adsorbates into the substrate and affects the electron properties of oxygen/ A III B V (111) interface.

Comparative experimental and theoretical studies of the fluorine/oxygen ratio influence on the structural and electronic properties of the anodic layer (AL)/InAs interface by XPS, HRTEM, C–V (77K) measurements and ab initio calculation of fluorine and oxygen adsorption on the InAs(111)­A-(1 × 1) unreconstructed surface were performed. The well-ordered transition layer (TL), composed of indium and arsenic oxyfluorides, and extension of the interplanar distance at the fluorinated anodic layer (FAL)/InAs interface were experimentally revealed. The theoretical modeling of AL/InAs and FAL/InAs interfaces showed that the fluorinated TR formation removes the InAs surface distortion, whereas the In­(InAs)–F–As­(FAL) and In­(InAs)–O–As­(FAL) bond formation is a reason for the interplanar distance increase between FAL and the InAs surface. The decrease of the interface state density in the InAs bandgap and the Fermi level unpinning at the FAL/InAs interface result from the positive charge increase on FAL arsenic atoms near the InAs surface during the As–F bonds formation, while the electron accumulation on oxygen atoms and InAs subsurface arsenic atoms is the reason for the states appearance in the InAs bandgap at the anodic (native) oxide/InAs interface.

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