Structure and composition analysis of the Cu–Zn–Se ternary compounds by TEM/EDS

Abstract

The structure and chemical composition of Cu1−xZn1−ySe2−δ (Cu–Zn–Se) ternary alloy semiconductors were examined by transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS), a TEM/EDS analytical technique. Polycrystalline Cu–Zn–Se thin films were prepared by atmospheric pressure metal–organic chemical vapor deposition. The TEM/EDS technique has made an elemental analysis focused on a microscopic region possible. Therefore, the spatial distribution of constituent elements of Cu–Zn–Se polycrystal within both grains and grain boundaries could be investigated and the compound stoichiometry was evaluated. Conclusively, the cross-sectional TEM images characterized the fabricated Cu–Zn–Se layers as a polycrystalline film of about 70–80nm thick and composed of grains with sizes ranging from 0.3 to 1.7μm. The chalcopyrite structure of Cu–Zn–Se films was confirmed by the selected area electron diffraction patterns. Moreover, the EDS point analyses conducted at optionally chosen positions showed quite comparable chemical compositions for the grains examined, yielding an average composition ratio of about 0.92:1.44:2 for Cu:Zn:(Se+O) within grains. However, the replacement of Cu atoms for Zn atoms in elemental composition was found at grain boundaries, resulting in an average composition ratio of about 1.26:1.24:2 for Cu:Zn:(Se+O) over there. It is suggested that the enhanced diffusion of Cu along the grain boundaries and the segregation of Cu to the grain boundaries increase the mean composition of Cu at these paths.