BAND-GAP ENGINEERING IN CU(IN,GA)SE-2 THIN-FILMS GROWN FROM (IN,GA)(2)SE-3 PRECURSORS

A three-stage process starting with the deposition of (In,Ga)(2)Se-3 p recursor films has been successful in the fabrication of graded band-g ap Cu(In,Ga)Se-2 thin films. In this work we examine (1) the reaction of Cu + Se with (In,Ga)(2)Se-3, which leads to a spontaneous grading i n the Ga content as a function of depth through the film, and (2) modi fication of the Ga content in the surface region of the film through a final deposition of In + Ga + Se. We show how band-gap grading can be enhanced by the formation of non-uniform precursors, how counterdiffu sion limits the degree of grading possible in the surface region, and how the CuxSe secondary phase acts to homogenize the film composition.