Mechanisms of Step-Stress Degradation in Carbon-Doped 0.15-μm AlGaN/GaN HEMTs for Power RF Applications
Nicolò Zagni, Z. Gao, G. Verzellesi, Alessandro Chini, A. Pantellini, Marco Natali, Andrea Lucibello, L. Latessa, C. Lanzieri, Carlo De Santi, Matteo Meneghini, Gaudenzio Meneghesso, Enrico Zanoni
Abstract
We discuss the degradation mechanisms of C-doped 0.15-μm gate AlGaN/GaN HEMTs tested by drain step-stress experiments. Experimental results show that these devices exhibit cumulative degradation effects during the step stress experiments in terms of either (i) transconductance (gm) decrease without any threshold-voltage (VT) change under OFF-state stress, or (ii) both VT and gm decrease under ON-state stress conditions. To aid the interpretation of the experiments, two-dimensional hydrodynamic device simulations were carried out. Based on obtained results, we attribute the gm decrease accumulating under OFF-state stress to hole emission from CN acceptor traps in the gate-drain access region of the buffer, resulting in an increase in the drain access resistance. On the other hand, under ON-state stress, channel hot electrons are suggested to be injected into the buffer under the gate and in the gate-drain region where they can be captured by CN traps, leading to VT and gm degradation, respectively.