Using polarization field effect-based thermionic field emission (PFE-TFE) model based on current-voltage-temperature data, possible carrier transport mechanisms for Pt/Au and Cr/Pd Schottky contacts to Al0.25Ga0.75N/GaN layers were investigated. Thermionic emission (TE) model was also investigated to compare to the PFE-TFE. It was shown that Schottky barrier heights (SBHs) are significantly affected by a polarization field-induced carrier density of the AlGaN layer. In addition, relatively little temperature dependence on the leakage current density of both contacts was found, which is in good agreement with the PFE-TFE model. The results indicate that the TFE is responsible for the current flow across the metal/AlGaN-GaN interface at T >= 293 K. (C) 2012 Elsevier B. V. All rights reserved.