Computer simulation of current transport in GaN and AlGaN Schottky diodes based on thin surface barrier model

Abstract

This paper attempts a rigorous computer simulation of the current transport in GaN and AlGaN Schottky diodes on the basis of the thin surface barrier (TSB) model recently proposed by the authors’ group. First, a computer program was developed which can calculate current transport through an arbitrary potential profile of Schottky barrier by a combined mechanism of thermionic emission (TE), thermionic-field emission (TFE) and field emission (FE). Then, from the view point of the TSB model, attempts were made to fit the theoretical temperature dependent current voltage (I–V–T) curves to the measured I–V–T data taken on Ni/n-GaN and Ni/n-AlGaN Schottky diodes changing the barrier profiles and the energy depth of the surface donor. As compared with the previous poor fitting using approximate analytic formulas, excellent fitting was obtained for both forward and reverse current, confirming the validity of the TSB model as the mechanism for anomalously large leakage currents in GaN and AlGaN Schottky diodes. Best fittings for GaN and Al0.26Ga0.74N were obtained for exponentially decaying distributions of surface defect donors with the peak density of 5 × 1018cm−3 and 1 × 1019cm−3, the characteristic decay depth of 11nm and 11.5nm and the energy depth of 0.25eV and 0.37eV, respectively.