We present the comparative study on AlN codoped ZnO (ANZO) and Al doped ZnO (AZO) thin films of different concentrations (0.5-4 mol%) grown by RF magnetron sputtering. X-ray diffraction (XRD), reflectance and Hall measurements have been carried out on both codoped ANZO and monodoped AZO films grown on Si (1 0 0) substrates. XRD studies reveal that all the films in both systems are polycrystalline. Further, it has been inferred that all the Al-doped films are under compressive strain while in the AlN-doped (codoped) films, 0.5 and 1 mol% are under tensile strain and others are in compressive strain. The reflectance measurements suggest that the optical band gap increases with Al concentration in monodoped systems whereas the band gap decreases upto 1 mol% and then increases for codoped system. The Hall measurements indicate that interestingly 0.5 and 1 mol% codoped ZnO films exhibit p-type conduction and obviously all the monodoped films show n-type conduction. FTIR spectra also confirm the larger density of Al-N bonds in p-ZnO films of codoped system. (C) 2008 Elsevier B. V. All rights reserved.