X-Ray Irradiation-Induced <i>V</i>TH Instability in Schottky-Gate p-GaN HEMTs

p-GaN Schottky-gate structure E-mode HEMTs have great potential for irradiation applications, yet their 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 is still under investigation. In this work, by constructing an X-ray irradiation online monitoring system with adjustable dose and integrated peripheral bias circuit, irradiation dose- and drain bias-dependent <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 are comprehensively investigated. Under irradiation-only conditions, the device exhibits 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">${V} _{\text {TH}}$ </tex-math></inline-formula> shift with low-dose irradiation, followed by 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 with high-dose irradiation. By performing numerical simulations, Hall measurements, and C–V tests, it is revealed that the 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 is dominated by the p-GaN activation-induced <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 mechanism, rather than the gate-related hole injection mechanism. The corresponding activation efficiency of p-GaN increases from 1.3% (unirradiated device) to 1.5% (0.11-Sv irradiation). Furthermore, acceptor-like defects are identified as the main cause of 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. The low-frequency 1/f noise experimental results show that the density of defect states at different doses is higher than that of unirradiated devices. Moreover, under the synergistic effect of irradiation and drain bias, the device still exhibits 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, which can be explained by the modified charge storage mechanism. These results provide important insights into the <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 Schottky-gate structure high electron mobility transistors (p-GaN HEMTs) under irradiation conditions.