Annealing effect on the structural, optical, and electrical properties of CuAlO₂ films deposited by magnetron sputtering

We studied the annealing effect on the structural, optical, and electrical properties of sputtered CuAlO₂ films. It is found that the crystallinity of CuAlO₂ films is improved with increasing the annealing temperature in N₂ ambient, and the film annealed at 900 °C presents the excellent preferred (001) orientation in X-ray diffraction patterns as well as Raman scattering signals, A_1g and E_g. The optical absorption edge of the annealed films is observed extremely complex. Four optical bandgaps estimated are distributed in the following energy regions: ~3.00, ~3.15, ~3.50, and ~3.75 eV, which might originate from different direct transitions in CuAlO₂ energy band, respectively. For the annealed CuAlO₂ films, the resistivity decreases three orders of magnitude, which is attributed to the contribution of intrinsic defects, Cu vacancy and interstitial oxygen.