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Using the measured capacitance-voltage curves and the photocurrent spectrum obtained from the Ni Schottky contact on a strained Al0.3Ga0.7N/GaN heterostructure, the value of the relative permittivity of the AlGaN barrier layer was analysed and calculated by self-consistently solving Schrodinger's and Poisson's equations. It is shown that the calculated values of the relative permittivity are different from those formerly reported, and reverse biasing the Ni Schottky contact has an influence on the value of the relative permittivity. As the reverse bias increases from 0 V to - 3 V, the value of the relative permittivity decreases from 7.184 to 7.093.

The thermal stability of strained AlGaN/GaN heterostructures is characterized by comparing unannealed and 700°C 30-min annealed Ni Schottky contacts prepared on strained AlGaN/GaN heterostructures. Using photoemission, capacitance–voltage measurements, and the self-consistent solution of Schrodinger's and Poisson's equations, it is found that after 700°C 30-min thermal annealing the Schottky barrier height of Ni Schottky contacts on strained AlGaN/GaN heterostructures is increased, and the sheet density of polarization charges and the sheet density of two-dimensional electron gas (2DEG) electrons for the strained AlGaN/GaN heterostructures are reduced. These results are closely related to the performance of AlGaN/GaN HFETs at high temperature.

An Ni/Au Schottky contact on an AlGaN/GaN heterostructure has been prepared. By using the peak-conductance model, the threshold voltage and the series resistance of the AlGaN/GaN diode are simultaneously extracted from the conductance—voltage (G—V) curve and found to be in good agreement with the ones obtained by using the capacitance—voltage (C—V) curve integration and the plot of dV/d(ln I) versus current I. Thus, a method of directly and simultaneously extracting both the threshold voltage and the series resistance from the conductance—voltage curve for the AlGaN/GaN Schottky diode is developed.

Ni/Au Schottky contacts with thicknesses of either 50 A/50 A or 600 A/2000 A were deposited on strained Al0.3Ga0.7N/GaN heterostructures. Using the measured C-V curves and I-V characteristics at room temperature, the calculated density of the two-dimensional electron-gas (2DEG) of the 600 A/2000 A thick Ni/Au Schottky contact is about 9.13 × 1012 cm−2 and that of the 50 A/50 A. thick Ni/Au Schottky contact is only about 4.77 × 1012 cm−2. The saturated current increases from 60.88 to 86.34 mA at a bias of 20 V as the thickness of the Ni/Au Schottky contact increases from 50 A/50 A to 600 A/2000 A. By self-consistently solving Schrodinger's and Poisson's equations, the polarization charge sheet density of the two samples was calculated, and the calculated results show that the polarization in the AlGaN barrier layer for the thick Ni/Au Schottky contact is stronger than the thin one. Thus, we attribute the results to the increased biaxial tensile stress in the Al0.3 Ga0.7N barrier layer induced by the 600 A/2000 A thick Ni/Au Schottky contact.