Iodine treatment of semiconductor surfaces

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GaAs and CuInS_2 surfaces treated with NH_4I have been studied by X-ray photoemission spectroscopy.GaAs substrate dipped in an aqueous solution of NH_4I was measured by XPS using monochromatized Al Kalpha x-ray. We found three chemical states of gallium from the Ga 3d apectra : (a) peaks from GaAs, (b) peaks which are 0.9 eV-deeper than those of GaAs, and (c) peaks which are 1.6 eV-deeper. Although the peaks (b) may be that of gallium iodide, at least the peaks (c) are considered to be gallium oxide, which can not be avoided by adjusting treatment paremeters. When the GaAs treated with NH_4I is heated in vacuum. iodide as well as oxide is removed from the surface. The iodide, however, sublimates earlier than the oxide. We thus conclude that the NH_4I treatment is not enough to avoid an oxidation of GaAs surfaces. We also studied the electrical properties of the NH_4I-treated GaAs surfaces. No significant change has been observed in the Schotkey barrier height.NH_4I solution, which is used to deposit CdS on CuInS_2, does also remove Cu oxide from CuInS_2 surface.