Role of excess cadmium in the electrical properties of devices made of chemically deposited nano-CdS

Effects of excess cadmium in chemically deposited cadmium sulfide (CdS) nanoclusters are investigated here. This was done by fabricating a bulk-nano (bn) junction of CdS and observing the alterations in the junction characteristics under different conditions. The I–V characteristics of such junctions clearly depict changes even with incident photon energy lesser than the HOMO-LUMO separation of nano-CdS, that are not stimulating the original electronic properties of either bulk or nano-CdS. Alterations of characteristics under such conditions assures the role of impurities like excess cadmium and oxygen in the sample. From the different junctions of bulk and nano-CdS, it is studied here that the excess Cd present in the sample could have raised the Fermi level of the nano layer and is responsible for the ohmic contact between nano-CdS and the tin oxide layer. The raise of the conduction level of nano-CdS roughly estimated here is in agreement with the suggestion that the excess cadmium in the chemically deposited nano-CdS causes a larger shift in the conduction band than that of its valance band.