The growth of nonpolar a-plane GaN on r-plane sapphire by metalorganic vapor-phase epitaxy has been investigated using a low-temperature nucleation layer (LT-NL) and using direct growth without a LT-NL The dislocation densities in a-plane GaN films can be reduced significantly from (6.2 +/- 0.3) x 10(10) cm(-2) to (2.1 +/- 0.3) x 10(9) cm(-2) using direct growth. The dislocation densities can also be reduced from (6.2 +/- 0.3) x 10(10) cm(-2) to (2.1 +/- 0.3) x 10(9) cm(-2) by introducing a SiN(x) interlayer into the film grown with a LT-NL However, introducing a similar SiN(x) interlayer into the film grown without a LT-NL produces no further dislocation reduction. Both the SiN(x) interlayers and the growth without a LT-NL reduce the dislocation density through the formation of islands, which promote dislocation bending and annihilation. (C) 2011 Published by Elsevier B.V.