Scanning capacitance microscopy of AlGaN/GaN heterostructure field-effect transistor epitaxial layer structures

Scanning capacitance microscopy is used to characterize local electronic properties in an Al_xGa_1-xN/GaN heterostructure field-effect transistor epitaxial layer structure. Lateral inhomogeneity in electronic properties is clearly observed, at length scales ranging from ∼0.1 to >2 μm, in images obtained at fixed bias voltages. Acquisition of a series of images over a wide range of bias voltages allows local electronic structure to be probed with nanoscale spatial resolution both laterally and in depth. Combined with theoretical analysis of charge and potential distributions in the epitaxial layer structure under applied bias, these studies suggest that the dominant factor contributing to the observed variations in electronic structure is local lateral variations in Al_xGa_1-xN layer thickness.