Forward Current Transport Mechanisms of Ni/Au–InAlN/AlN/GaN Schottky Diodes

We fabricate two Ni/Au-In_0.17Al_0.83N/AlN/GaN Schottky diodes on substrates of sapphire and Si, respectively, and investigate their forward-bias current transport mechanisms by temperature-dependent current-voltage measurements. 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 1.413 eV 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.