p-CdS:Cu/n-CdS thin-film diodes showed light emission of bright green by deposition of a Us layer at a high substrate temperature and by the use of an TTO/SnO2-coated glass substrate. XPS analysis showed that indium diffused into the CdS:Cu layer from the ITO layer at the ITO/CdS:Cu interface but that indium did not diffuse into the CdS:Cu layer at the ITO/SnO2/CdS:Cu interface. Indium compensates the acceptor of Cu as a donor in Us. The tin oxide layer prevented diffusion of In into Us. Again, the deposition of Us at a high substrate temperature may promote activation of Cu as an acceptor, and the Cu may form shallow acceptor levels. Therefore, it is thought that the bright green emission from the ITO/SnO2-based diodes is due to shallow Cu acceptor levels. (c) 2004 Elsevier B.V. All rights reserved.