Increasing threshold voltage and reducing leakage of AlGaN/GaN HEMTs using dual-layer SiN x stressors

In this work, AlGaN/GaN HEMTs with dual-layer SiNx stressors (composed of a low-stress layer and a high-stress layer) were investigated. The low-stress padding layer solved the surface damage problem which was caused during the deposition of the high-stress SiNx and provided a good passivated interface. The HEMTs with the dual-layer stressors showed a 1 V increase in the threshold voltage (Vth) with comparable DC and RF amplification performance to the baseline devices. Moreover, the off-current (Ioff) was shown to be reduced by one to three orders of magnitude in the strained devices. The reduction in the off-currents was a result of the lower electric field in AlGaN, which suppressed the gate injection current. These improvements using the dual-layer stressor scheme supports strain engineering as an effective approach in the pursuit of the normally-off operation of AlGaN/GaN HEMTs.