Nanometer-Thick Insertion Layer for the Effective Passivation of Surface Traps and Improved Edge Acuity for AlGaN/GaN HEMTs

In AlGaN/GaN high electron mobility transistors (HEMTs), the existence of long lifetime surface traps can cause several adverse effects, including threshold voltage (V-th) instability and current collapse. Therefore, understanding the nature and lifetime of these traps is crucial to provide effective passivation. In this work, the nature of these traps is scrutinized by combining femtosecond transient optical and multiple structural analyses. Later, using a nanometer-thick Al2O3 insertion layer, these traps are effectively passivated. In order to observe the effect of the proposed passivation on device performance, HEMT devices were fabricated. As a result of this passivation, better edge acuity in ohmic contacts and protection of the surface of the epitaxy were achieved. The lag performance of the HEMT devices was significantly improved. It was found that the drain lag was reduced from 37.1% (for the standard SiNx passivated design) to 10.4% for the modified HEMT design. In operating this transistor as a power amplifier, nearly no change in the quiescent bias point was observed after consecutive load-pull measurements, which shows the stability of the fabricated device.