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 Cd_1- Cu₂₍Se where x is the atom% of Cu₂Se doped into CdSe) for lower wt% of Cu₂Se, and nanocomposites of Cd_1- Cu₂₍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 Cd_1- Cu₂₍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.