Microstructural Characterization of High Indium-Composition InXGa1−XN Epilayers Grown on c-Plane Sapphire Substrates

The growth of high-quality indium ~In!-rich InXGa1 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 InXGa1 XN alloys are inevitable phenomena that degrade the crystal quality of In-rich InXGa1 XN layers. Composition modulations were observed in the In-rich InXGa1 XN layers with various In compositions. The In composition modulation in the InXGa1 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 In0.67Ga0.33N/ GaN interface. The composition modulations were formed on the specific crystallographic planes of both the $0001% and $0 N 114% planes of InGaN.