Surface charging effects on current stability of AlGaN/GaN HEMTs

Using a dual-gate transistor structure, we have evaluated the effect of off-bias-stress spatially induced surface charging at the AlGaN/GaN surface. Pulsed voltage stress on the drain access region led only to increase in the on-resistance, whereas the stress on the source region additionally decreased the saturation drain current. In addition, significant surface charging in the access region resulted in a threshold voltage shift. The 2D potential simulation indicated that surface negative charges modulate the potential distribution near the gate edge. It was also found that such surface charging can extend as far as 0.5 μm from the stressing gate edge.