Current Kink Effect in β-Ga₂O₃ MOSFETs Induced by Incomplete Ionization of Donors

In this article, the origin of severe drain–source current kink effect in <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga₂O₃ MOSFETs has been exploited by means of temperature- and pulse-dependent current–voltage (I–V) analysis. By reducing the pulse biasing widths, whereby the self-heating effect was negligible, the output characteristics were free of kink but with a rather low drain–source current density (<inline-formula> <tex-math notation="LaTeX">${I}_{\text {DS}}$ </tex-math></inline-formula>) at a high drain voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula>) of 30 V. The current kink effect started to occur with a direct-current power consumption of approximately 850 mW/mm. The elimination of kink features was also observed together with a large <inline-formula> <tex-math notation="LaTeX">${I}_{\text {DS}}$ </tex-math></inline-formula> at elevated temperatures over 100 °C. These observations indicate that the kink effect is strongly related to thermal activation of incomplete ionized donors by either the self-heating effect or external intentional heating stress rather than high electric field. In terms of temperature-dependent current output characteristics, the thermal activation energy is determined to be 136 meV, which is consistent with the reported unintentional donors with a high activation energy of 110 meV. It implies that additional electrons are thermally activated and emitted from the incomplete ionized donors in <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga₂O₃ channel or buffer layers through the self-heating effect, contributing to the channel conductivity modulation and the consequent current kink effect. These findings may bridge the knowledge gap between charge transport mechanisms and the reliability degradation of <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga₂O₃ power switches.