Nonpolar (1 1 (2) over bar 0) and semipolar (1 1 (2) over bar 2) GaN films were grown on sapphire by metalorganic vapour phase epitaxy using ScN interlayers of varying thicknesses. A 5 nm interlayer reduced basal plane stacking fault (BSF) densities in nonpolar films by a factor of 2 and threading dislocation (TD) densities by a factor of 100 to (1.8 +/-0.2) x 10(9) cm(-2). An 8.5 nm interlayer reduced BSF densities in semipolar films by a factor of 5 and reduced TD densities by a factor of 200 to (1.5 +/- 0.3) x 10(8) cm(-2). Nonpolar film surface roughnesses were reduced by a factor of 20. (C) 2009 Elsevier B.V. All rights reserved.