Improvement in the light emission characteristics of CdS:Cu/CdS diodes

p-CdS:Cu/n-CdS thin-film diodes showed light emission of bright green by deposition of a CdS layer at a high substrate temperature and by the use of an ITO/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 CdS. The tin oxide layer prevented diffusion of In into CdS. Again, the deposition of CdS 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.