Extraction of Polarization-Induced Charge Density in Modulation-Doped AlxGa1-xN/GaN Heterostructures Based on Schottky C-V Simulation

A method based on Schottky capacitance-voltage (C-V) simulation was developed to extract the polarization-induced charge density in modulation-doped AlxGa1-xN/GaN heterostructures. There are two characteristic slopes in the experimental and simulated C-V curves.The influences of the polarization-induced charge density, n-AlGaN doping level and the Schottky barrier height on the positions of the two slopes in the C-V curves are much different from each other. The polarization-induced charge density can be extracted accurately by fitting the experimental C-V curves. It is extracted to be 6.78 x 1012cm-2in modulation-doped Al0.22Ga0.78N/GaN heterostructures with the Al0.22Ga0.78N thickness of 30 nm or 45 nm. The charge density reducesto 1.30 x 1012cm-2in the heterostructure with the Al0.22Ga0.78N thickness of 75 nm. It is thought that the reduction of the polarization-induced charges at the heterointerface is due to the partial relaxation of the Al0.22Ga0.78N layer on GaN.