Improvement of the Enhancement-Mode GaN MIS-HEMTs by Fluorine Doping in the Dielectric Gate Stack

This study tested fluorine doping on various regions of the ferroelectric charge trap gate stack (FEG stack). Fluorine doping effectively reduces oxygen vacancies in the dielectric layer, thus reducing leakage current and stabilizing charge in the dielectric layer. Moreover, fluorine doping can passivate the dangling bonds at the interface and increase the ability of trapping carriers in the trap layer. The FEG stack comprises a tunnel oxide layer (TL), a charge trap layer (CTL), and a ferroelectric layer (FE). Four types of devices were fabricated: undoped, doping in TL, doping in CTL, and doping in both TL and CTL, to investigate the impact of fluorine doping on the FEG gate stack. Devices doping in TL and CTL demonstrated superior performance, achieving the highest V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> of 5.4 V with a retention time of 70.42% after 10, 000 seconds. The off-state and gate leakage tests revealed impressive breakdown voltages of 735 V and 24.55 V, respectively. Furthermore, the device exhibited a high operation voltage of 14.3 V for a 10-year lifetime prediction, enabling a wide operating range.