Localized variations in electronic structure of AlGaN/GaN heterostructures grown by molecular-beam epitaxy

Local electronic properties in a molecular-beam-epitaxy-grown AlxGa1−xN/GaN heterostructure field-effect transistor epitaxial layer structure are probed using depth-resolved scanning capacitance microscopy. Theoretical analysis of contrast observed in scanning capacitance images acquired over a range of bias voltages is used to assess the possible structural origins of local inhomogeneities in electronic structure, which are shown to be concentrated in areas where Ga droplets had formed on the surface during growth. Within these regions, there are significant variations in the local electronic structure that are attributed to variations in both AlxGa1−xN layer thickness and Al composition. Increased charge trapping is also observed in these regions.