Role of Carbon in dynamic effects and reliability of 0.15 um AlGaN/GaN HEMTs for RF power amplifiers

This paper presents results concerning the dynamic performance and reliability of Fe-doped and C-doped 0.15-mu m gate AlGaN/GaN HEMTs. Step-stress tests at increasing drain-source voltage and different gate-source voltages are specifically reported. Fe-doped HEMTs exhibit, under both off- and on-state conditions, excellent parametric stability up to breakdown. C-doped devices are instead affected by enhanced degradation effects during the step stress experiments compared to Fe-doped ones, consisting of R-ON increase during off-state stress and both threshold-voltage and R-ON increase under on-state conditions. 2D hydrodynamic device simulations are used to validate hypotheses on the physical mechanisms underlying the observed, distinctive degradation effects. The role of C doping in causing additional degradation compared to Fe-doped device is explained with the aid of device simulations as follows: 1) under off-state conditions, hole emission from the C-N acceptor traps in the gate-drain region of the buffer leads to an R-ON increase which is not completely recovered during the typical recovery time interval following each stress phase and therefore accumulates during the step stress experiment; 2) under on-state conditions, channel hot electrons are injected (besides towards the surface) into the buffer where they can be captured by C-N traps under the gate and in the gate-drain region, inducing semi-permanent threshold-voltage and R-ON increases.