Gate-Localized Fluorination Enables Enhancement-Mode AlGaN/GaN High-Electron Mobility Transistors

Area of Science:

• Materials Science
• Semiconductor Device Physics

Background:

• Gallium Nitride (GaN)-based High-Electron-Mobility Transistors (HEMTs) are crucial for high-power and high-frequency applications.
• Enhancement-mode (E-mode) operation is desired for power switching due to failsafe behavior and reduced standby power.
• Traditional E-mode fabrication methods present challenges like complexity, surface damage, and instability.

Purpose of the Study:

• To develop a simplified and stable fabrication process for normally off AlGaN/GaN HEMTs.
• To address the limitations of conventional E-mode enhancement strategies.

Main Methods:

• A gate-localized CHF3 plasma process was employed.
• This process created a self-limiting recess and a fluorine-terminated surface.
• Plasma exposure was confined to the gate region to minimize surface degradation.

Main Results:

• The process enabled normally off AlGaN/GaN HEMTs with a stable, positive shift in threshold voltage (Vth).
• Fluorine incorporation compensated polarization charges, while hydrogen passivated defects.
• Fabricated devices showed normally off operation with low gate leakage under bias stress.

Conclusions:

• The gate-localized CHF3 plasma process provides a practical and stable route to E-mode GaN HEMTs.
• This method avoids deep gate recessing, mitigating fabrication complexity and instability.
• The developed approach is suitable for energy-efficient, high-frequency, and high-power electronic systems.