Bowing of epitaxial layers grown on bulk GaN substrates

Abstract

We investigated the bowing of mixed group III nitride epitaxial layers grown by HVPE (Hydride Vapor Phase Epitaxy) and MOVPE (Metalorganic Vapor Phase Epitaxy) on bulk GaN substrates, grown at high pressure (HP). We measured the radius of bowing, lattice-mismatch (by X-Ray Diffraction), aluminum content (by XRD) and density of threading dislocations (by Defect Selective Etching) as a function of the layer thickness. The results section is divided into two parts. In Part I, we present the results for thick HVPE GaN layers mismatched to bulk HP GaN by 0.01–0.02%. We found the critical thickness for its plastic relaxation of about 30 µm, when grown on 60 µm thick HP GaN substrate. In Part II, thin MOVPE AlxGa1–xN layers are characterized. For most of these layers, the bowing is larger than predicted by theory, what suggests not equal elastic properties of AlGaN and HP bulk GaN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)