Unified mechanism of the surface Fermi level pinning in III-As nanowires

Fermi level pinning at the oxidized (110) surfaces of III-As nanowires (GaAs, InAs, InGaAs, AlGaAs) is studied. Using scanning gradient Kelvin probe microscopy, we show that the Fermi level at oxidized cleavage surfaces of ternary Al\(_{x}\)Ga\(_{1-x}\)As (0\(\le\)x\(\le\)0.45) and Ga\(_{x}\)In\(_{1-x}\)As (0\(\le\)x\(\le\)1) alloys is pinned at the same position of 4.8\(\pm\)0.1 eV with regard to the vacuum level. The finding implies a unified mechanism of the Fermi level pinning for such surfaces. Further investigation, performed by Raman scattering and photoluminescence spectroscopy, shows that photooxidation of the Al\(_{x}\)Ga\(_{1-x}\)As and Ga\(_{x}\)In\(_{1-x}\)As nanowires leads to the accumulation of an excess arsenic on their crystal surfaces which is accompanied by a strong decrease of the band-edge photoluminescence intensity. We conclude that the surface excess arsenic in crystalline or amorphous forms is responsible for the Fermi level pinning at oxidized (110) surfaces of III-As nanowires.