Effects of the surface Cu2−xSe phase on the growth and properties of CuInSe2 films

Abstract

Drastic changes in average molecularities (m=Cu/In) from m≫1 to m=0.92–0.93 and in hole concentrations from p≫1019 cm−3 to as low as p=7.5×1016 cm−3 have been observed in molecular beam epitaxy grown CuInSe2 after selective etching of the Cu–Se phase by a KCN aqueous solution; high hole concentrations and Cu-excess compositions of the as-grown films were attributed to the Cu–Se phase. On the other hand, well-defined photoluminescence emissions were found characteristic of intrinsic CuInSe2. The presence of the Cu–Se phase made possible the growth of high-quality CuInSe2 epitaxial films at a temperature well below the melting point of any Cu–Se compound. Surface topology measurements showed that the surface of the as-grown films was not fully covered by Cu–Se grains, leaving holes with depths of 200–300 nm after KCN etching. The enhanced two-dimensional growth and the reduced defect concentration imply that a very thin Cu-excess surface layer controls the growth of CuInSe2 when grown under Cu-excess conditions.