Observation of I<sub>D</sub>-V<sub>D</sub> Kink in N-Polar GaN MIS-HEMTs at Cryogenic Temperatures
Davide Bisi, Steven Wienecke, Brian Romanczyk, Haoran Li, Elaheh Ahmadi, S. Keller, Matthew Guidry, Carlo De Santi, Matteo Meneghini, Gaudenzio Meneghesso, Umesh K. Mishra, Enrico Zanoni
Abstract
This paper reports on the hot-carrier effects and semi-on-state behavior of nitrogen-polar GaN MIS-HEMTs at cryogenic temperatures (from 300 K down to 100 K). In the semi-on-state (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ≈ -2 V), holes are generated by impact ionization in the high field region at the drain-side of the gate-edge. At room temperature, holes overcome the SiN/AlGaN stack and are collected at the gate-terminal, resulting in measurable hole gate-current (~11 nA/mm). Conversely, at cryogenic temperatures, the top SiN/AlGaN stack confines the holes within the GaN channel, thus inducing a negative threshold voltage shift (-0.4 V) and a sharp increase in drain current (0.18 A/mm). This behavior, referred to as “kink,” is readily observable on the ID-VD characteristics. We demonstrated that the kink is related to impact ionization and follows a non-monotonic behavior maximized in the semi-on-state. Our interpretation is supported by a quantitative analysis based on the latest experimental impact-ionization coefficients available in the literature.