A study of different selenium sources in the synthesis processes of chalcopyrite semiconductors

In this work, we studied the selenization processes of sputtered Cu/In stacked layers with two different kinds of Selenium (Se) sources: Se pellets (A) and an evaporated layer (B). Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Grazing Incidence X-Ray Diffraction (GIXRD) and Raman spectroscopy were used to characterize the selenized films. In the group A, elemental Se pellets were used to generate Se vapor and react with metallic precursors. When selenized at 270 C, a large amount of Cu-Se platelets exhibiting regular hexagonal or polygonal structures were observed at the film surface. After the selenization at 380 C, the films were constituted of large CuInSe₂ grains with diameter in the 500 nm range. In the group B, an evaporated Se layer at the precursor surface was involved as Se source. At 270 C, the film surfaces were homogeneously covered by the Cu-Se wires. Energy Dispersive X-Ray Spectroscopy (EDS) and GIXRD both indicated that a Se concentration lower in the wires than that in the platelets formed in group A. At 380 C, films were made of a single CuInSe₂ phase, with grain sizes in the 200-300 nm range, i.e. smaller than the grain sizes of group A. The relationships of film surface modifications during the selenization with different Se sources were discussed.