Under a controlled As partial pressure, the nitridation process of GaAs(001)-(2 x 4) surface was studied using a scanning tunnelling microscope, combined with an electron cyclotron resonance plasma-assisted molecular beam epitaxy system. Upon prolonging the nitridation time, or decreasing the As partial pressure, the previously reported (3 x 3) structure, with two dimers per surface cell ((3 x 3)-2D) was found to progressively convert into a new (3 x 3) structure characterized by one dimer per surface cell ((3 x 3)-1D). Reversely the exposure to arsenic transformed the structure from (3 x 3)-1D to (3 x 3)-2D; suggesting that the top-most layer was composed of As2-dimers. Based upon these scanning tunnelling microscopic images, together with the X-ray photo-electron spectroscopy data, the new As2-dimer coverage model was proposed to explain both (3 x 3)-1D and -2D structures involving the exchange reaction of arsenic with nitrogen in the sub-surface region of GaAs.

Surface Reconstruction of GaAs(001) Nitrided under a Controlled As Partial Pressure. T.Imayoshi, H.Oigawa, H.Shigekawa, H.Tokumoto: Surface Science, 2003, 540[1], L577-82