Polarization-Induced Charges in Modulation-Doped AlxGa1-xN/GaN Heterostructures Through Capacitance-Voltage Profiling

Polarization-induced charges in modulation-doped Al 0.22 Ga 0.78 N/GaN heterostructures were investigated by the capacitance-voltage ( C - V ) method. The C - V profile of the Pt/Al 0.22 Ga 0.78 N/GaN Schottky diodes with various Al 0.22 Ga 0.78 N thicknesses shows significant differences due to change of the polarization field in the heterostructures. A numerical simulation based on the experimental results indicates that the sheet density of the polarization-induced charges at the heterointerface is 6.78 × 10 12 cm -2 in the samples with the Al 0.22 Ga 0.78 N thicknesses of 30 nm or 45 nm. The charge density reduces to 1.30 × 10 12 cm -2 in the sample with the Al 0.22 Ga 0.78 N 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 Al 0.22 Ga 0.78 N layer on GaN. This work provides a technique for quantitative characterization of the polarization-induced charges in Al x Ga 1- x N/GaN heterostructures.