Effect of Misorientation Angle of r-Plane Sapphire Substrate on a-Plane GaN Grown by Metalorganic Vapor Phase Epitaxy

Abstract

We investigated the effect of the misorientation angle of an r-plane sapphire substrate on a-plane GaN grown by metalorganic vapor phase epitaxy. The misorientation angle was changed systematically in the direction of the [0001] c-axis or [1100] m-axis (denoted θ1) and in the direction of the [1120] a-axis (denoted θ2). Results show that the surface morphology and crystalline quality are very sensitive to θ1 misorientation angle. We successfully grew an a-plane GaN layer with a pit-free surface by optimizing the misorientation angle of the r-plane sapphire substrate. We found that the r-plane sapphire substrate with a θ1 misorientation angle between -0.53 and -0.28° is very effective for growing a-plane GaN with a pit-free surface. Moreover, a θ1 misoriention angle between -0.53 and -0.28° improves crystalline quality in the GaN c-axis direction, but causes a slight increase in tilt mosaicity in the GaN m-axis direction. In contrast, a θ2 misorientation angle between -0.55 and +0.52° produces no differences in the surface morphology and crystalline quality of a-plane GaN.