Mechanisms of Step-Stress Degradation in Carbon-Doped 0.15-m AlGaN/GaN HEMTs for Power RF Applications

We discuss the degradation mechanisms of C-doped0.15-mu m 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 (g(m)) decrease without any threshold-voltage (V-T) change under OFF-state stress, or (ii) both V-T increase and g(m) decrease under ON-state stress conditions.To aid the interpretation of the experiments, two-dimensionalhydrodynamic device simulations were carried out. Based on theobtained results, we attribute the g(m )decrease accumulating underOFF-state stress to hole emission from C-N acceptor traps in thegate-drain access region of the buffer, resulting in an increase inthe drain access resistance. On the other hand, under ON-statestress, channel hot electrons are injected into the buffer underthe gate and in the gate-drain region where they are captured by C-N traps, leading to V(T )and g(m) degradation, respectively.