One-step direct fabrication of phase-pure Cu2O films via the spin-spray technique using a mixed alkaline solution

Abstract

The spin-spray technique was used to fabricate phase-pure Cu2O films at 70 °C with a high deposition rate of 0.3 μm/min. The source solution, containing a mixture of CuSO4･5H2O and l-ascorbic acid, and the reaction solution, containing NH3 and NaOH, were sprayed on the rotating substrates. It was possible to control the grain size, the crystalline orientation of the films, the surface morphology, and the optical band gap by adjusting the concentrations of NH3 and NaOH in the reaction solution. The films fabricated with a low NH3 aq. concentration were composed of nanosized grains and highly [111] oriented. On the other hand, films fabricated with a high NH3 aq. concentration were composed of submicron grains and highly [100] oriented. The surface morphologies of the films varied according to the concentration of NaOH. The surface of the films fabricated with a low NaOH concentration were almost flat and had a {100} orientation on their surface. On the other hand, films fabricated with a high NaOH concentration were composed of pyramidal grains. A smaller grain size in the films corresponded with a higher optical band gap.