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