We report a study on the role of substrate temperature (T-s), ranging from 850 to 1150 degrees C and the effect of ambient nitrogen pressure (5 x 10(-4) and 5 x 10(-5) Torr) on the structural and optical properties of pulsed laser deposited AlN thin films on c-axis Al2O3 substrates. It is found that along with the band gap of the pulsed laser-deposited AlN thin films, the crystallographic orientation turns from (10 (1) over bar 0) to (0 0 0 2) depending on the substrate temperature (T-s) and the ambient nitrogen pressure. At T-s = 850 degrees C and above-mentioned nitrogen pressures, the deposited thin films showed preferential orientation along (10 (1) over bar 0) and a band gap of about 5.4 eV. At higher T-s of 950 degrees C, both the orientation i.e. (10 (1) over bar 0) and (0 0 0 2) were observed. The variation in intensity of these orientations depends on the ambient nitrogen pressure. At 5 x 10(-4) Torr, both the orientations were observed with almost equal proportions and the band gap of the corresponding thin film was about 5.4eV. Interestingly, at lower pressure of 5 x 10-5 Torr the film, predominantly, showed orientation along (0 0 0 2) and the band gap of the corresponding film was about 5.9 eV. At even higher T-s = 1050 degrees C, even though the films were oriented mainly along (0002), the crystalline quality of the films deposited at 5 x 10(-5) Torr nitrogen pressure was much superior when compared to those deposited at 5 x 10(-4) Torr nitrogen pressure. Investigations of the thin films using atomic force microscopy and Raman spectroscopy support the above observations. Attempts have been made to explain the observations in terms of the temperature and pressure-dependent growth modes. (C) 2007 Elsevier B.V. All rights reserved.