Phase control of semi-polar (112¯2) and non-polar (112¯0) GaN on cone shaped r-plane patterned sapphire substrates

The control of formation of semi-polar (112¯2) and nonpolar a-plane (112¯0) 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°C and 200mbar, only semi-polar (112¯2) GaN is formed. Increasing the nucleation layer temperature to 965°C, only (112¯0) GaN is grown at 200mbar. At reduced reactor pressure of 60mbar, phase selectivity breaks down and semi-polar (112¯2) and non-polar (112¯0) GaN exist simultaneously. The crystalline quality of a-plane GaN on r-plane CPSS can be effectively improved using optimized growth direction control.