Composite formation in CdSe:Cu2Se nanocrystal films, charge transport characteristics and heterojunction performance

The use of nanocrystals as materials for potential technological applications depends on tailoring their properties through intentional doping with external impurities. We have used a new technique to synthesize nanocrystal thin films of CdSe:Cu2Se containing different weight percentages (wt%) of Cu2Se. The films were deposited on glass substrates at room temperature by co-evaporation of CdSe and Cu2Se powder in nitrogen gas at a pressure larger than that required for conventional thin film deposition. The films consisted of nanograins of CdSe doped with Cu2Se (i.e., nanograins of Cd1-xCu2(x)Se where x is the atom% of Cu2Se doped into CdSe) for lower wt% of Cu2Se, and nanocomposites of Cd1-xCu2(x)Se and Cu2Se for higher wt% of Cu2Se. An energy band diagram built using the Anderson model was used for discussing the heterojunction characteristics of the junction between nanograins of Cd1-xCu2(x)Se and Cu2Se. To investigate the usefulness of the nanocrystal thin films of CdSe:Cu2Se for practical applications, the I-V characteristics of p-p and p-n hetero-junctions formed by the films respectively with nanostructured films of similarly deposited Cu2Se and CdSe films were studied.