Single phase (11-22) GaN on (10-10) sapphire grown by metal-organic vapor phase epitaxy

Heteroeptaxial growth of semipolar GaN on (101_0) sapphire by metal-organic vapor phase epitaxy has been investigated using high temperature nucleation layers in order to provide large GaN templates for semipolar light emitters. The nitridation layer and nucleation conditions were optimized for phase pure {112_2} layer orientation, minimum surface roughness and improved crystal quality. Single phase {112_2} GaN layers were obtained by controlling the nitridation conditions and thus nitridation layer thickness. The crystal quality was improved by high temperature growth. Basal plane stacking faults were identified as the dominating defects by transmission electron microscopy. Photoluminescence measurements revealed that these defects are type I₁. A layer roughness of 4 nm was measured by atomic force microscopy.

Highlights

► Highest (11-22) GaN phase purity is found at 980°C nitridation and nucleation.

► Smoothest (11-22) layers are found for intermediate nitridation layer thicknesses.

► A reduced threading dislocation density is observed.