Growth of Cu(In,Ga)Se2 films using a Cu-poor/rich/poor sequence:: substrate temperature effects

Thin film Cu(In,Ga)Se-2 is grown using constant substrate temperatures and deposition times of less than 20 min for film thicknesses of 2 mum. In the growth process used, referred to as the CUPRO process, only the Cu flux varies, in such a manner that the film evolves from Cu-poor to Cu-rich to Cu-poor. The evolution of the film is monitored by tracking the change in the thermal response of the substrate. Films and devices are produced using a given evolution of the Cu content and their quality and characteristics are correlated to the substrate temperature, between 475 and 550 degreesC. The films are analysed by scanning electron microscopy and X-ray diffraction (XRD), the devices by current-voltage and quantum efficiency (I(V) and QE(lambda)) measurements. Morphologically, the bottom fraction of the layers, grown prior to the film becoming Cu-rich, does not appear to be very temperature dependent, whereas differences are observed in the upper fraction, which result from the Cu-rich and back to Cu-poor stages of the growth. From the device parameters a shift in the bandgap of the Cu(In,Ga)Se-2 with substrate temperature is found. The XRD study shows (220)(204) orientation of the films grown at the lower temperatures. Total area device efficiencies up to 15.5%, without AR, have been obtained, without large impact of the substrate temperature. (C) 2003 Elsevier Science B.V. All rights reserved.