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

Drastic changes in average molecularities (m = Cu/In) from m much greater than 1 to m = 0.92-0.93 and in hole concentrations from p much greater than 10(19) cm(-3) to as low as p = 7.5 x 10(16) 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. (C) 1999 American Institute of Physics. [S0003-6951(99)01011-6].