Lateral variations in threshold voltage of an AlxGa1-xN/GaN heterostructure field-effect transistor measured by scanning capacitance spectroscopy

Local dC/dV spectroscopy performed in a scanning capacitance microscope (SC M) was used to map, quantitatively and with high spatial resolution (simila r to 50 nm), lateral variations in the threshold voltage of an AlxGa1-xN/Ga N heterostructure field-effect transistor epitaxial layer structure. Scanni ng capacitance and the associated threshold voltage images show small round features less than 150 nm in diameter with a corresponding shift in thresh old voltage of about 1.5-2 V, and larger features several microns in size w ith a corresponding shift in threshold voltage of approximately 1 V. The sm all features in the SCM and threshold voltage images are consistent with th e presence of charged threading dislocations, while the variations in thres hold voltage over large areas could be a result of thickness and/or composi tion variations in the AlxGa1-xN layer. (C) 2001 American Institute of Phys ics.