Quantitative analysis of nanoscale electronic properties in an AlxGa1-xN/GaN heterostructure field-effect transistor structure

Local dC/dV spectroscopy performed in a scanning capacitance microscope is used to map. quantitatively and with high spatial resolution, lateral varia tions in the threshold voltage of an AlxGa1-xN/GaN heterostructure field-ef fect transistor epitaxial layer structure. Theoretical analysis and numeric al simulations are used to quantify charge concentrations, the correspondin g threshold voltage shifts, and the influence of the measurement apparatus on these results. High-resolution scanning capacitance and the associated t hreshold voltage images reveal round features < 150 nm in diameter within w hich a shift in threshold voltage of about 1.5-2 V is measured. Theoretical analysis and numerical simulations indicate that these features are consis tent with the presence of charged threading dislocations with a linear char ge density of similar to 10(7) e/cm(-1) that cause localized partial or ful l depletion of carriers from the two-dimensional electron gas. Large-scale scanning capacitance images reveal variations in contrast over areas severa l microns in size with corresponding threshold voltage shifts of approximat ely I V. These large features are postulated to arise from a combination of thickness and composition variations in the AlxGa1-xN layer. (C) 2001 Amer ican Vacuum Society.