Shih-Chang Liang

Characterization and optoelectronic properties of p-type N-doped CuAlO2 films

This letter reports a technique for increasing the carrier concentration and the conductivity of the p-type CuAlO2 through doping the material with nitrogen. The x-ray photoelectron spectroscopy and the optical band gap analyses suggested that the nitrogen atoms occupying the interstitial sites of the delafossite structure provided the p-type CuAlO2 with an impurity energy level in the energy gap. It was also found that the N-doped CuAlO2 film had its optimum conduction properties when the dopant level reached 1.1at.%. Here, the carrier concentration was raised from 4.81×1016 in the undoped film to 2.13×1017cm−3 in the doped film, and the corresponding film’s conductivity was increased from 3.8×10−2to5.4×10−2(Ωcm)−1, as compared with the undoped CuAlO2 film.

Phase Transformation and Optoelectronic Properties of p-Type CuAlO2 Thin Films

Annealed Cu-Al-O films showed marked structural changes and differing optoelectronic properties with varying annealing temperature. Results of X-ray diffraction (XRD) demonstrated that CuO and CuAl 2 O 4 were the intermediate reaction phases. XRD also showed that the phase grown above 800°C annealing temperature was pure CuAlO 2 phase. Cross-sectional high-resolution transmission electron microscopy revealed that the crystallization behavior of the Cu-Al-O films belonged to an outward model. The optimum properties of delafossite structure CuAlO 2 film was attained after annealing at 800°C. The surface morphology of CuAlO 2 had a cell-like surface appearance and the grain sizes were approximately 20-100 nm. The optical direct bandgap of the CuAlO 2 film was estimated to be 3.11 eV. Hall effect measurements revealed that the CuAlO 2 film belonged to the p-type conduction category, with a carrier concentration of 4.81 X 10 16 cm -3 and the conductivity of 3.8 × 10 -2 (Ω cm) -1 . The optoelectronic properties of the Cu-Al-O system are dominated by the delafossite CuAlO 2 .