V T Shift and Recovery Mechanisms of p-GaN Gate HEMTs Under DC/AC Gate Stress Investigated by Fast Sweeping Characterization

Abstract

In this work, details of stress time dependent transient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {T}}$ </tex-math></inline-formula> shift in p-GaN Gate HEMTs are captured using a fast sweeping method. A minimum saturated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {T}}$ </tex-math></inline-formula> shift ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{\text {T}\_{}\text {Sat}}$ </tex-math></inline-formula> ) independent of stress time at about 4 V gate stress is observed, and electron tunneling process assisted by shallow traps in the AlGaN barrier is introduced as a likely mechanism to explain the phenomena. Under gate stress of 6 V and above, a stress time dependent over-recovery results in a negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {T}}$ </tex-math></inline-formula> shift before the final recovery to the fresh state, confirming that hole de-trapping process needs to take a longer time than electron de-trapping process. In addition, under AC gate stress condition, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{\text {T}\_{}\text {Sat}}$ </tex-math></inline-formula> shows an opposite trend in cases of low and high forward AC gate bias stresses, which is explained by the difference in the trapping rates of electrons and holes.