Microstructural Characterization of High Indium-Composition In_XGa_1−XN Epilayers Grown on c-Plane Sapphire Substrates

Abstract The growth of high-quality indium (In)-rich In_XGa_1−XN alloys is technologically important for applications to attain highly efficient green light-emitting diodes and solar cells. However, phase separation and composition modulation in In-rich In_XGa_1−XN alloys are inevitable phenomena that degrade the crystal quality of In-rich In_XGa_1−XN layers. Composition modulations were observed in the In-rich In_XGa_1−XN layers with various In compositions. The In composition modulation in the In_XGa_1−XN alloys formed in samples with In compositions exceeding 47%. The misfit strain between the InGaN layer and the GaN buffer retarded the composition modulation, which resulted in the formation of modulated regions 100 nm above the In_0.67Ga_0.33N/GaN interface. The composition modulations were formed on the specific crystallographic planes of both the {0001} and {0114} planes of InGaN.