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-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 RON increase during off-state stress and both threshold-voltage and RON 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 CN acceptor traps in the gate-drain region of the buffer leads to an RON 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 CN traps under the gate and in the gate-drain region, inducing semi-permanent threshold-voltage and RON increases.