Physical origin of current collapse in Au-free AlGaN/GaN Schottky Barrier Diodes

Dynamic characterization (Pulsed I-V) on Au-free AlGaN/GaN Schottky Barrier Diodes (SBDs) has been performed to evaluate the impact of negative quiescent bias on the forward characteristics. Results show an increase of on-resistance when more negative quiescent biases are applied, and a sudden current collapse phenomenon when the quiescent bias exceeds -175 V. Furthermore, the measurements show a common signature: the total current collapse is the result of the trapping phenomena occurring around the Schottky contact corner. The trap levels of 0.5 eV and 1.0 eV have been characterized from current transient spectroscopy. A TCAD model with these two trap levels as donor states at the Si3N4/AlGaN interface has been defined, to understand their role and explain the observed behavior of AlGaN/GaN SBDs from this dynamic measurement. We propose that trapping at deep energy levels (Trap1=1.0 eV), existing at the Si3N4/AlGaN interface, is responsible for the gradual current reduction observed for negative quiescent biases up to Anode-to-Cathode voltage of -175 V. The electron filling of the shallower traps with high density at energy level located 0.5 eV below the conduction band starts at higher reverse biases, resulting in a strong Fermi-level pinning, which can be the cause of sudden current collapse.