NOVELTY - A method of forming a copper-indium-gallium sulfide and selenide semiconductor layer on a base (21) involves growing a conductive layer on a substrate (22) to form a base; depositing on it a metallic film (24) comprising copper; electroplating a gallium film (26) over the it; electroplating an indium film (25) over the gallium film, to provide a precursor stack (20) that has an indium-rich top surface with a melting temperature higher than that of gallium; and reacting the precursor stack with at least one of selenium and sulfur.    USE - For preparing metallic precursor thin films for the growth of semiconductor compounds to be used for radiation detector and solar cell fabrication.    ADVANTAGE - The method efficiently uses expensive materials necessary for the making of solar cells. The method utilizes a PVD method for the deposition of the low cost component of the compound, i.e. copper, and uses electro-deposition for the expensive components, i.e. indium (In) and gallium (Ga). In this way, adhesion and nucleation challenges for electroplating copper on the contact layer such as molybdenum can be avoided, and also near 100% materials utilization of electro-deposition provides important cost advantages for the deposition of the expensive Ga and In.    DETAILED DESCRIPTION - A method of forming a copper-indium-gallium sulfide and selenide (Cu(In,Ga)(S,Se)2) semiconductor layer on a base (21) involves growing a conductive layer on a substrate (22) to form a base; depositing on it a metallic film (24) comprising copper; electroplating a gallium film (26) over the it; electroplating an indium film (25) over the gallium film, to provide a precursor stack (20) that has an indium-rich top surface with a melting temperature of higher than that of gallium; and reacting the precursor stack with at least one of selenium and sulfur. The depositing a first film comprising only copper on the base uses a physical vapor deposition method.    DESCRIPTION OF DRAWING(S) - The figure shows a metallic precursor stack of Cu/In/Ga.    stack (20)    base (21)    substrate (22)    copper layer (24)    indium layer (25)    gallium layer. (26)