We fabricate two Ni/Au-Ino.17 Al0.83N/AlN/GaN Schottky diodes on substrates of sapphire and Si,respectively,and investigate their forward-bias current transport mechanisms by temperature-dependent current-voltage mea-surements.In the temperature range of 300-485 K,the Schottky barrier heights (SBHs) calculated by using the conventional thermionic-emission (TE) model are strongly positively dependent on temperature,which is in contrast to the negative-temperature-dependent characteristic of traditional semiconductor Schottky diodes.By fitting the forward-bias Ⅰ-Ⅴ characteristics using different current transport models,we find that the tunneling current model can describe generally the Ⅰ-Ⅴ behaviors in the entire measured range of temperature.Under the high forward bias,the traditional TE mechanism also gives a good fit to the measured Ⅰ-Ⅴ data,and the actual barrier heights calculated according to the fitting TE curve are 1.434 and 1.413eV at 300 K for InAlN/AlN/GaN Schottky diodes on Si and the sapphire substrate,respectively,and the barrier height shows a slightly negative temperature coefficient.In addition,a formula is given to estimate SBHs of Ni/Au-InAlN/AlN/GaN Schottky diodes taking the Fermi-level pinning effect into account.