Cu(In,Ga)Se2 thin films grown with a Cu-poor/rich/poor sequence:: Growth model and structural considerations

Thin films of Cu(In,Ga)Se-2 are grown by a co-evaporation process in which the In, Ga, and Se fluxes, as well as the substrate temperature, are constant and the only variable is the Cu flux. This Cu flux varies in three steps in such a way that the growing film evolves from Cu-poor to Cu-rich and then back to Cu-poor. The film growth is monitored by the 'end point detection' method, and film thicknesses of the order of 2 mum are deposited in less than 20 min. Quality devices (efficiencies above 151,10) are produced in our baseline processes for all of the other synthesis steps. The Cu(In, Ga)Se2 layers are studied from a (112) versus (220) (204) orientation and recrystallization point of view. Including the results from a previous study on the influence of the substrate temperature to the present X-ray diffraction and scanning as well as tunneling electron microscopy data, a five-stage growth model for the films is described. The specific features of these films are that they are weakly (220) (204) oriented and exhibit crevices in their top fractions. The growth model hypothesizes about the origins of these crevices and on how to avoid them. Copyright (C) 2003 John Wiley Sons, Ltd.