PBTI in GaN-HEMTs With p-Type Gate: Role of the Aluminum Content on $Δ VTH and Underlying Degradation Mechanisms

In this paper, we present an experimental analysis of the degradation induced by positive bias temperature instability stress in GaN-based power high electron mobility transistors with p-type gate, controlled by a Schottky metal/p-GaN junction. In particular, the role of the aluminum content (Al%) in the AlGaN barrier layer on the threshold voltage degradation is investigated by means of constant voltage stress measurements. This has been performed for different process conditions with varying Al content. Main results in this paper demonstrate that when a relatively large positive bias is applied on the gate, two competing trapping mechanisms take place in the AlGaN barrier layer or at the p-GaN/AlGaN interface causing VTH instability. First, an aluminum independent hole trapping mechanism, caused by elastic tunneling from p-GaN valence band (2-D hole gas), leads to a relatively short-time and recoverable negative VTH shift. In the second step, defect creation occurs. These additional defects are filled with electrons and cause a permanent or slowly recoverable positive VTH degradation. The amount of defect creation was dependent on the Al% in the barrier.