Optical and Electrical Properties of Magnetron Sputtering Deposited Cu–Al–O Thin Films

We have successfully prepared Cu–Al–O films on silicon (100) and quartz substrates with copper and aluminum composite target by using radio frequency (RF) magnetron sputtering method. We have related the structural and optical-electrical properties of the films to the sputtering area ratio of Cu/Al for the target (rCu/Al). The deposition rate of the film and rCu/Al can be fitted by an exponential function. rCu/Al plays a critical role in the final phase constitution and the preferred growth orientation of the CuAlO2 phase, thus affecting the film surface morphology significantly. The film with main phase of CuAlO2 has been obtained with rCu/Al of 45%. The films show p-type conductivity. With the increase of rCu/Al, the electrical resistivity decreases first and afterwards increases again. With rCu/Al of 45%, the optimum electrical resistivity of 80 Ω·cm is obtained, with the optical transmittance being 72%–79% in the visible region (400–760 nm). The corresponding direct band gap and indirect band gap are estimated to be 3.6 eV and 1.7 eV, respectively.