Aluminium-nitride thin films were deposited on silicon Si(111) substrate with pulsed laser deposition in a Riber LDM-32 system. The optical properties of the films were studied by means of optical spectroscopy with an incoherent light source mainly covering the visible range. It is demonstrated that, in comparison with an aluminium mirror, under certain deposition conditions, the film may behave as a metallic thin film as far as the optical reflection is concerned. In this case, there is an enhanced plasmonic reflection peak in the optical spectrum and the peak may be modified according to the degree of the phase transition. The microscopic structures as well as the surface topographies of the films were also studied with X-ray photoelectron spectroscopy and scanning electron microscopy. It turns out that the density and the size of the microscopic domains in the film determine whether the film remains dielectric or becomes metallic. The diamagnetic effect in the enhanced plasma increases in the process when the sample is smoothed out with the optimized nitrogen gas pressure. The nitrogen pressure is thus identified as the most influential deposition condition to the phase transition. © 2009 Elsevier B.V. All rights reserved.