Effect of a Cu-Se secondary phase on the epitaxial growth of CuInSe2 on (1Â 0Â 0) GaAs

The effect of a secondary copper selenide phase that appears during epitaxial growth of CuInSe2 (CIS) films on (1 0 0) GaAs substrates was investigated. CIS films with different copper to indium molar ratios were deposited on (1 0 0) GaAs substrates at 360 °C by migration-enhanced epitaxy. Films grown under In-rich conditions were polycrystalline, whereas films grown with a Cu-rich composition were epitaxial, as evidenced by pole figure analysis, even when the copper composition was only slightly higher than the 1:1 Cu:In molar ratio. The epitaxial film growth followed a Stranski-Krastanov mode and contained both matrix and island regions. Grazing incidence XRD revealed a small amount of CIS with the Cu-Au-like structure near the surface of the island regions. A binary Cu-Se secondary phase aggregated near the surface in the island regions of the film, as determined by electron probe microanalysis (EPMA) before and after etching in 10% KCN. It is proposed that a Cu-Se phase present during the growth of Cu-rich CIS films enhances the mobility of adatoms on the substrate surface, allowing the film to grow epitaxially to a critical thickness. After that critical thickness is attained, the Cu-Se phase segregates at dislocation sites to nucleate the island regions. TEM-EDX scans of cross-sections also suggested a small amount of the Cu-Se secondary phase segregates on the film surface.