Band-gap engineering in Cu(In,Ga)Se/sub 2/ thin films grown from (In,Ga)/sub 2/Se/sub 3/ precursors

A three-stage process starting with the deposition of (In,Ga)/sub 2/Se/sub 3/ precursor films has been successful in the fabrication of graded band-gap Cu(In,Ga)Se/sub 2/ thin films. In this work we examine (1) the reaction of Cu+Se with (In,Ga)/sub 2/Se/sub 3/, which leads to a spontaneous grading in the Ga content as a function of depth through the film, and (2) modification 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 nonuniform precursors, how counterdiffusion limits the degree of grading possible in the surface region, and how the Cu/sub x/Se secondary phase acts to homogenize the film composition.