We report Al3+ and large radii mismatched As5+ codoped p-ZnO thin films by As back diffusion from GaAs substrate and sputtering Al2O3 (1, 2 and 4 at%) mixed ZnO target. Hall effect measurements showed that the hole concentration increased upon codoping (As5+ and Al3+) compared to the monodoped (As5+) film. Also, it showed that 1 at% Al doped ZnO:As has low resistivity with high hole concentration due to best codoping. The crystallinity of the films has been studied by X-ray diffraction. The p-type formation mechanism has been investigated by X-ray photoelectron spectroscopy and low temperature photoluminescence analysis. It implies that As5+ substitutes on Zn2+ instead on O2- site that leads to the formation of (As-Zn-2V(Zn)) complex which gives rise to p-conductivity. Further, the fabricated p-n homojunction using best codoped p-ZnO film shows typical rectifying characteristics of a diode. (C) 2012 Elsevier B.V. All rights reserved.