Epitaxy of ternary nitrides on GaN single crystals

InxGa1-xN and AlxGa1-xN layers were grown by metalorganic chemical vapour d eposition (MOCVD) on highly conductive single crystals of GaN. The samples were then examined using X-ray diffraction and photoluminescence. It was fo und that there is a substantial difference in properties between the layers grown on the N-face (00.{(1) under bar}), chemically active, and Ga-face ( 00.1), chemically inert, sides. The latter layers had smaller free-electron concentration, better crystallographic quality and different chemical comp ositions. All the examined layers were fully strained, even for 1.1% lattic e mismatch between the GaN substrate and about 0.1 mu m thick In0.11Ga0.88N layer. The half-widths of the photoluminesce (PL) dominant peaks correspon d to the compositional gradients observed in X-ray diffraction. The positio ns of the PL peaks agree with the X-ray data if bowing parameters of 3.2 eV for InGaN layers and 0.25 eV for AlGaN layers were used. (C) 1999 Elsevier Science B.V. All rights reserved.