Observation and Analysis of Anomalous <i>V</i> <sub>TH</sub> Shift of p-GaN Gate HEMTs Under off-State Drain Stress
Xin Chao, Chengkang Tang, Chen Wang, Jingjing Tan, Ji Li, Lin Chen, Hao Zhu, Qingqing Sun, David Wei Zhang
Abstract
In this work, time-dependent threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> ) instability of p-GaN gate high electron mobility transistors (HEMTs) under OFF-state drain stress is systematically investigated. An anomalous <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> shift behavior is observed with an initial negative shift followed by a kink and a positive shift upon prolonged stress time. Through bias- and temperature-dependent stress/recovery experiments, it has been found that the process of electron releasing by donor states at the p-GaN/AlGaN and AlGaN/GaN interface is the primary reason for negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> shift in the initial stage. The hole deficiency in the p-GaN layer gradually dominates the change in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> and finally leads to a positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> shift. Moreover, a continual leakage path between the gate and drain terminal during the stress stage is further revealed which is mainly ascribed to the trap-assisted electron tunneling across the AlGaN layer. In addition, the effect of OFF-state drain stress on static ON-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text{ON}}$ </tex-math></inline-formula> ) is also studied, and it is found that the trapped electrons at the passivation/AlGaN interface and/or in the GaN buffer layer results in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text{ON}}$ </tex-math></inline-formula> degradation.