Abstract

This study compares Vth-instability in D-mode MIS-HEMT devices between 2-epitaxial layers, AlN/AlGaN/GaN superlattice-W1, and three-step graded AlGaN-W2. Experimental results demonstrate that W1 exhibits ∼13% less Vth-instability compared to W2, with distinct degradation regions at specific voltage ranges. With temperature variation (30°C-150°C), these regions justified and reveal small positive Vth-shifts due to electron trapping, leading to temporary degradation, followed-by negative Vth-shifts from positive charge injection, culminating in catastrophic degradation attributing impact ionization at 30°C during 0-30V gate-step stress, with permanent failure observed. Analysis indicates W1-devices are more efficient and stable. Also, both layers operate reliably till VGS=18V, with ∼3% minor Vth-instability.

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