Carrier Transport Mechanisms Underlying the Bidirectional &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${V}_{\mathrm{{TH}}}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Shift in p-GaN Gate HEMTs Under Forward Gate Stress

Yuanyuan Shi,Dong Wei,Pengcheng Wei,Qi Zhou,Wanjun Chen,Bo Zhang,Qian Cheng,Liyang Zhu,Anbang Zhang

doi:10.1109/ted.2018.2883573

Abstract

The threshold voltage (V TH ) instability of p-GaN/AlGaN/GaN HEMTs was investigated under forward gate stress. A unique bidirectional V TH shift (AV TH ) with the critical gate voltage (V G ) of 6 V was observed. The carrier transport mechanisms underlying the AV TH were extensively investigated through the voltage-dependent, timeresolved, and temperature-dependentgate current. The gate current is decomposed into electron and hole current in three distinct regions with respect to V G , which are off-state for V G <; 1.2 V (V TH ), on-state for 1.2 V <; V G <; 5 V and “gate-injected” region for V G > 5 V. In off-state, the electrons were thermally activated and transport towards the gate, while electron-trapping governed by the space charge limited conduction (SCLC) in AlGaN barrier was observed in on-state and “gate-injected” region. Such an electrontrapping effect results in the positive V TH shift for V G <; 6 V. Meanwhile, the marginal hole transport from gate by thermal activation was also captured by gate current, which features negligible impact on V TH . However, for V G > 6 V, a drastic hole injection triggered by high V G takes place that causes subsequent hole-trapping in AlGaN barrier and holeinjection into GaN buffer. The injected holes enhance the positive charge in the gate region and turned the positively shifted V TH into a negative shift.

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