Investigation of Off-State Stress-Induced Nonuniform Trapping Phenomenon in p-Type GaN High Electron Mobility Transistors (HEMTs)

This study discusses the nonuniform electron trapping behavior under OFF-state stress (OSS) in p-gallium nitride (GaN) high electron mobility transistors (HEMTs). The subthreshold swing (SS) degradation is generated from the punchthrough current induced by the nonuniform electron trapping into the AlGaN layer. Technology computer-aided design (TCAD) simulations are performed to replicate the electric field distribution across the device and the electric potential distribution along the channel under OSS. The simulation results indicate a strong electric field exists at the gate/p-GaN/AlGaN stack of the drain side. Accordingly, a depletion region is generated in the p-GaN layer, leading to electron trapping in the AlGaN layer of the drain side. Subsequently, a physical model is proposed to explain the trapping mechanism. Moreover, the degradation behavior of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>D</i></sub>-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>G</i></sub> transfer characteristics and the two-step turn-on behavior of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>GS</roman></sub>-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>G</i></sub> transfer curve further validate the presence of a nonuniform trapping phenomenon.