Au Schottky diodes were prepared by vacuum evaporation or by plasma sputtering on n-AlGaN(Si) films with Al mole fractions of 0, 0.11 or 0.23. The barrier heights were deduced from C-V and I-T measurements. The difference between the C-V and I-T results was less than 0.1 eV for the barriers deposited at 300 °C on HF etched samles with prior in situ heating at 450 °C. For low deposition temperatures (about 150°C) C-V and I-T methods give results differing by some tenths of an eV. For deposition temperatures exceeding 450°C the diodes were very leaky. The barrier heights were 0.8 eV, 0. 9 eV and 1.1 eV for AlGaN with compositions of 0, 0.11 and 0.23. For plasma sputtered diodes on GaN and AlGaN (x=0.11) samples, the difference in C-V and I-T results was quite considerable and admittance spectroscopy indicated the presence of deep electron traps at 0.12-0.14 eV that were absent in vacuum evaporated diodes. For similar diodes on AlGaN(x=0.23) samples the results of C-V and I-T measurements were very close and no traps at 0.12-0.14 eV could be detected. This difference is most likely due to damage caused by low energy ions. More Al-rich films are less susceptible to such damage. Persistent photocapacitance was observed in n-AlGaN Schottky diodes after illumination at 85K.