AlN layers grown by magnetron sputter epitaxy (MSE) are effective buffer layers for the growth of high quality GaN materials and devices. The structural and morphological properties of AlN layers with two different thicknesses (20 and 200 nm) grown by this technique were analyzed by atomic force microscopy and X-ray diffraction measurements. The root-mean-square surface roughness of the MSE AlN layers was 0.625 nm for the 20 nm thick AlN layer, and 0.249 nm for the 200 nm thick one. In the latter, however, scattered hexagonal plateaus (up to 200 nm in diameter and 10 nm in height) were found embedded in the otherwise atomically smooth surface. The MSE AlN layers were found to be single crystalline epilayers in c-axis orientation, with crystalline quality better or comparable to AlN layers grown by ammonia-molecular-beam epitaxy (MBE) with similar thicknesses. Compared with the MBE counterparts, the MSE AlN layers showed smaller compressive strain at the 20 nm thickness, and crossed into tensile strain at the 200 nm thickness. (C) 2002 Elsevier Science B.V. All rights reserved.