COMPOSITIONAL INHOMOGENEITY OF INGAN GROWN ON SAPPHIRE AND BULK GAN SUBSTRATES BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION

The compositional inhomogeneity of the InGaN layers in GaN/InGaN/GaN d ouble-hetero (DH) and InGaN/GaN single-hetero (SH) structures grown by metalorganic chemical vapor deposition ((MOCVD) on sapphire (0001) an d bulk GaN was investigated by means of cathodoluminescence (CL) and e nergy dispersive X-ray (EDX) spectroscopy. Dotlike CL image of the ban d edge emission from InGaN was observed. The bright spots were found t o have higher indium content compared to that on the outside of the sp ots. The compositional inhomogeneity increased and the density of the spot decreased with increasing film thickness. Hexagonal hillocks, whi ch had higher indium content and emitted stronger CL, were observed on the surface of the SH structure. Compositional inhomogeneity of homoe pitaxial InGaN on bulk GaN substrate was much less compared to that of InGaN on sapphire revealing that dislocation plays a key role in prod ucing an inhomogeneity. A possible mechanism that explains these pheno mena is proposed.