Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

The influence of electric field (EF) on the dynamic ON-resistance (dyn-R-DS[ON]) and threshold-voltage shift (Delta Vth) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (I-DS-V-DS) and drain current (I-D) transients. Different EF was realized with devices of different gate-drain spacing (L-gd) under the same OFF-state stress. Under high-EF (L-gd = 2 mu m), the devices exhibited higher dyn-R-DS[ON] degradation but a small Delta Vth (similar to 120 mV). However, at low-EF (L-gd = 5 mu m), smaller dyn-R-DS[ON] degradation but a larger Delta Vth (similar to 380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-R-DS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing Delta Vth. A trap with activation energy 0.33 eV was identified in the AlGaN barrier by I-D-transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations. (C) 2015 AIP Publishing LLC.