The forward current-voltage I(V) characteristics of (Ni-Au)/ Al_0.25Ga_0.75N/GaN/SiC structures with differentSchottky contact  areas were determined in the temperature range of 50-320K. The estimated values of ideality factor (n), zero-bias barrier height  and series resistance (Rs) assuming thermionic emission (TE) show a  temperature dependence of these parameters. Moreover, the conventional Richardson plot of  versus  for each sample shows two linear regions in the temperature ranges of 50-230K and 230-320K. The obtained Richardson constant values  are lower than the theoretical value  for Al_0.25Ga_0.75N. Such behavior was attributed to Schottky barrier inhomogeneities by assuming a double Gaussian distribution (GD) of the barrier heights (BHs) at the (Ni-Au)/Al_0.25Ga_0.75N interface. We attempted to draw  versus  plot in order to obtain evidence of the double GD of BHs for each sample. Therefore, the temperature dependence of the forward I(V)characteristics can be successfully explained on the basis of the TE theory with a double GD of the BHs at (Ni-Au)/Al_0.25Ga_0.75N interface. These results suggest that the lateral inhomogeneity of the Schottky barrier height (SBH) is connected to the non-uniform distribution of surface and/or interface states. This non-uniformity is attributed to the presence of defects which confirms the results already obtained by capacitance deep level transient spectroscopy (DLTS) technique.

AlGaN/GaN heterostructures, barrier inhomogeneity,deep traps,Schottky contact areas.