The effects on surface morphology, crystal quality, and growth rate of undoped AlN layers grown on c-plane sapphire substrates due to the changes in growth parameters, such as V-III ratio, N-2-H-2 ratio, and growth temperature in LP-MOVPE are studied here. The optimized growth process resulted in an almost flat surface morphology with a significantly reduced number of hexagonal pits (3 x 10(7) cm(-2)) and good crystalline quality having a rms value of roughness of 0.4 urn measured by atomic force microscopy and a high resolution X-ray diffraction (HRXRD) FWHM value for (0002) reflection of 200 aresecs. The threading dislocation density of the AlN layer is estimated approx. 10(9) cm(-2) from cross-sectional transmission electron microscopy (TEM) measurements. Additionally, these optimized samples show a strong donor-bound exciton luminescence signal with a FWHM of 20 meV. Furthermore, small period AlN/GaN superlattice structures with excellent uniformity were grown, as proven by our HRXRD and TEM studies. (c) 2006 Elsevier B.V. All rights reserved.