Microstructural properties and atomic arrangements in GaN/sapphire and Al_xGa_1-xN/AlN/GaN/sapphire heterostructures

Microstructural and atomic structure studies of GaN/sapphire and A _xGa_1-xN/AlN/GaN heterointerfaces have been performed by using bright-field transmission electron microscopy (TEM) and selected area electron diffraction pattern (SADP) measurements. TEM and SADP results from the GaN/sapphire and the Al_0.4Ga_0.6N/AlN/GaN/sapphire heterointerfaces showed that GaN epilayers and Al_0.4Ga _0.6N, AlN, and GaN active layers, respectively, had been grown on the sapphire substrates. The values of the strain and the stress in the Al _0.4Ga_0.6N, the AlN, and the GaN layers were determined. Possible schematic diagrams of the two heterostructures, as well as diagrams of the [21̄1̄0] projections of the GaN epilayer and the Al _0.4Ga_0.6N/AlN/GaN heterostructure, are presented based on the TEM and SADP results. These results can help improve the understanding of the microstructural properties of the strained Al_xGa _1-xN/AlN/GaN/sapphire heterostructures for applications in the high-speed and high-power electronic devices.