Local electronic properties of AlGaN/GaN heterostructures probed by scanning capacitance microscopy

Local electronic properties in AlxGa1-xN/GaN heterostructure field-effect t ransistor epitaxial layer structures are probed using scanning capacitance microscopy. Acquisition of scanning capacitance images over a wide range of bias voltages combined with theoretical analysis and numerical simulation allows the presence, detailed nature, and possible structural origins of na nometer- to micronscale inhomogeneities in electronic structure to be eluci dated. Substantial lateral variations in local threshold voltages for trans istor channel formation are observed, at length scales ranging from submicr on to >2 mu m, and found to arise primarily from local variations in AlxGa1 -xN layer thickness. Features in electronic structure are also observed tha t are consistent with the existence of networks of negatively charged threa ding edge dislocations, as might be formed at island coalescence boundaries during epitaxial growth. The negative charge associated with these structu res appears to lead to local depletion of carriers from the channel in the AlxGa1-xN/GaN transistor epitaxial layer structure.