Electro-optical characteristics and field-emission properties of reactive DC-sputtered p-CuAlO2+x thin films

P-type transparent-conducting CuAlO2+x thin films were deposited on silicon and glass substrates by reactive direct current sputtering of a prefabricated metal powder target having 1:1 atomic ratio of Cu and Al in oxygen-diluted argon atmosphere. XRD spectrum confirmed the proper phase formation of the material. UV-Vis-NIR spectrophotometric measurements showed high transparency of the films in the visible region with direct and indirect band gap values around 3.90 and 1.89 eV, respectively. The room temperature conductivity of the film was of the order of 0.22 S cm-1 and the activation energy was ∼0.25 eV. Seebeck coefficient at room temperature showed a value of +115 μV/K confirming the p-type nature of the film. Room temperature Hall effect measurement also indicated positive value of Hall coefficient with a carrier concentration ∼4.4x1017 cm-3. We have also observed the low macroscopic field emission, from the wide band gap p-CuAlO2+x thin film deposited on glass substrate. The emission properties have been studied for different anode-sample spacing. The threshold field was found to be as low as around 0.5-1.1 V/μm. This low threshold is attributed primarily to the internal nanostructure of the thin film, which causes considerable geometrical field enhancement inside the film as well as at the film/vacuum interface