The initial and subsequent stages of growth of AlN on 4H-SiC (1 1 2 0) and GaN on AlN (1 1 2 0) have been investigated using atomic force microscopy and X-ray photoelectron spectroscopy. The AlN nucleated and grew via the Stranski-Krastanov mode. Densely packed, [0 0 0 1]-oriented individual islands were observed at 10 nm. Additional deposition resulted in the gradual reorientation of the growth microstructure along the [1 1 0 0]. GaN formed via the Volmer-Weber mode with rapid growth of islands along the [1 1 0 0] to near surface coverage at a thickness of 2 nm. Continued deposition resulted in both faster vertical growth along [1 1 2 0] relative to the lateral growth along [0 0 0 1] and a [1 1 0 0]-oriented microstructure containing rows of GaN. Fully dense GaN films developed between 100 and 250 nm of growth, and the preferred in-plane orientation changed to [0 0 0 1]. Lateral growth of GaN films reduced the dislocation density from similar to 4 x 10(10) to similar to 2 x 10(8) cm(-2). The high concentration of stacking faults (similar to 10(6) cm(-1)) was also reduced two orders of magnitude. (c) 2006 Elsevier B.V. All rights reserved.