Spectromicroscopic investigation of (NH4)(2)S treated polycrystalline Cu(In1-xCax)Se-2

Device-grade polycrystalline thin-film Cu(In1-xGax)Se-2 was treated with (N H4)(2)S at 60 degrees C to determine the resulting microscopic surface comp osition/morphology. Scanning electron microscopy was used to evaluate the r esultant macroscopic surface morphology. Modification of the surface and gr ain boundary chemistry of the Cu(In1-xGax)Se-2 polycrystalline films was in vestigated with scanning photoemission spectromicroscopy. The submicrometer lateral resolution of this technique allows us to directly characterize no t only the surface chemistry of the treated films on the submicron scale, b ut also to probe the grain boundary chemistry. Chemical maps depicting the distribution of chemical species on the surface and at grain boundaries wer e obtained by monitoring the S 2p, Se 3d, In 4d/Ga 3d and Cu 3d (valence ba nd) photoelectrons while scanning the sample. Background maps were also acq uired of each of the peak energies to separate chemical contrast from topog raphic contrast. Results show that S has been incorporated at the surface, possibly creating a wider bandgap Cu(In1-xGax)(Se1-ySy)(2) surface layer, a nd along the grain boundaries. The purpose of this investigation is to find an environmentally safe replacement for the toxic CdS overlayer commonly u sed for heterojunction devices without sacrificing overall device performan ce and reliability. (C) 1999 Elsevier Science B.V. All rights reserved.