High temperature current transport in gate oxides based (GaN)/AlGaN/GaN Schottky diodes

We have prepared high temperature stable Schottky MOS diodes on AlGaN/GaN heterostructure with Ir-Al oxide based gate oxide layer and analyzed current transport mechanism in these diodes up to very high temperatures. The thermionic emission analysis of I-V curves gave high ideality factor in between 2 and 3 decreasing with increasing temperature. Simulation of the thermionic transport with the barrier height extracted from the measured curves and ideality factor unity gave the simulated current densities many orders of magnitude higher than experimentally measured. We explained experimental data by a bias dependent barrier height as a result of thin dielectric layer and a bias dependent charge localized in interface traps between the semiconductor and this dielectric layer. The measured data are then explained by the thin dielectric layer at the interface between (GaN)AlGaN and the metal electrode. Increasing forward voltage and moving Fermi level towards conduction band the charge in the traps becomes negative and increases the effective barrier height for electrons moving from the semiconductor into the metal. By this mechanism also a linear increase of reverse current with bias can be explained. The opposite is true for the reverse voltage.