Analysis and control of excess leakage currents in nitride-based Schottky diodes based on thin surface barrier model

Using a rigorous computer simulation program for current transport through a Schottky barrier with an arbitrary potential profile, the leakage current mechanism in GaN and AlGaN Schottky diodes was investigated on the basis of the thin surface barrier (TSB) model recently proposed by the authors' group. Computer simulation assuming various possible defect density distributions was carried out to reproduce the measured temperature dependent current voltage. (I-V)-temperature characteristics of the GaN and AlGaN Schottky diodes which showed excessive reverse leakage. By assuming exponentially decaying distributions from surface for defect donors with energy depth of 0.25 eV for GaN and 0.37 eV for Al0.15Ga0.85N, I-V curves measured by our group as well as reported in the literatures were almost completely reproduced both in forward and reverse direction over a wide temperature range. The defect donors are proposed to be N vacancies or their related complexes that are formed during metal deposition. The result confirms the validity of the TSB model. From the viewpoint of the TSB model, attempts were also made to suppress leakage currents. It was found that a low-energy electrochemical metal deposition process and a metal-insulator-semiconductor Schottky structure using an ultrathin Al2O3 film by electron cyclotron resonance oxidation of Al film were remarkably effective in reducing excess leakage currents due to reduction of defect deep donors.