NOVELTY - A workpiece having a precursor layer on a substrate (11) is provided. The precursor layer comprising copper, indium, gallium, selenium and dopant, is heated to temperature (I) and reacted in selenium vapors at temperature (I) for time (I) to form absorber structure. The selenium vapors are removed and absorber structure is cooled to temperature (II). Temperature (I) is greater than temperature (II). The absorber structure is reacted in an inert gas atmosphere at temperature (II) for time (II), to form a group IB-IIIA-VIA absorber layer (12).    USE - Formation of group IB-IIIA-VIA (copper-indium-gallium selenide) absorber layer for manufacturing photovoltaic cells e.g. solar cells. Can also be used for radiation detectors.    ADVANTAGE - The method enables formation of high-quality thin films, which enables highly efficient fabrication of solar cells, while maintaining minimal interference from the substrate. The copper-indium-gallium selenide layers produced by the two-step process provides the ability to produce a large grain structure which extends from top to bottom of the film with a relatively uniform gallium distribution. Due to the short time spent at high-temperature regime of first reaction, deleterious substrate effects are minimized.    DETAILED DESCRIPTION - A workpiece having a precursor layer formed over a substrate is provided. The precursor layer comprises copper, indium, gallium, selenium, and a dopant including a group IA material. The precursor layer is heated to temperature (I) and reacted in selenium vapors at temperature (I) for time (I) to transform the precursor layer to a partially formed absorber structure. The selenium vapors are removed after reaction and the partially formed absorber structure is cooled to temperature (II). Temperature (I) and temperature (II) are each above 400 degrees C, and temperature (I) is greater than temperature (II). The partially formed absorber structure is reacted in an inert gas atmosphere at temperature (II) for time (II), which is longer than time (I), to form a group IB-IIIA-VIA absorber layer.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a solar cell.    Substrate (11)    Absorber layer (12)    Conductive layer (13)    Transparent layer (14)    Radiation (15)