The control of formation of semi-polar (11 (2) over bar2) and nonpolar a-plane (11 (2) over bar0) GaN phases on r-plane cone shaped patterned sapphire substrates (CPSS) by metalorganic vapor-phase epitaxy has been investigated. With a nucleation layer grown at 535 degrees C and 200 mbar, only semi-polar (11 (2) over bar2) GaN is formed. Increasing the nucleation layer temperature to 965 degrees C, only (11 (2) over bar0) GaN is grown at 200 mbar. At reduced reactor pressure of 60 mbar, phase selectivity breaks down and semi-polar (11 (2) over bar2) and non-polar (11 (2) over bar0) GaN exist simultaneously. The crystalline quality of a-plane GaN on r-plane CPSS can be effectively improved using optimized growth direction control. (C) 2013 Elsevier B.V. All rights reserved.