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

## TL;DR

A new method using fluorine plasma improves GaN transistors for better performance in high-power electronics.

## Contribution

A gate-localized fluorination process enables stable enhancement-mode GaN HEMTs without deep recessing or surface damage.

## Key findings

- Fluorine-terminated surfaces enable normally off operation with positive threshold voltage shifts.
- Hydrogen species from plasma passivate defects and reduce interface traps.
- Gate-localized fluorination avoids surface degradation and maintains low gate leakage.

## Abstract

Gallium nitride (GaN)-based
high-electron-mobility transistors
(HEMTs) are key to high-power and high-frequency electronics owing
to their wide bandgap, high breakdown field, and ability to form a
high-density two-dimensional electron gas (2DEG) at the AlGaN/GaN
interface. For power-switching systems, enhancement-mode (E-mode)
operation, where devices remain normally off at zero gate bias, is
preferred for intrinsic failsafe behavior and reduced standby power.
However, conventional E-mode strategies, such as deep gate recessing
or p-type gate insertion, often introduce fabrication complexity,
surface damage, and long-term instability. Here, we demonstrate a
gate-localized CHF3 plasma process that simultaneously
produces a self-limiting recess with a fluorine-terminated surface,
enabling a normally off AlGaN/GaN HEMT. Fluorine incorporation compensates
polarization-induced charges and drives a positive shift in threshold
voltage (V
th), whereas hydrogen species
generated during plasma exposure passivate etch-induced Ga-related
defects and suppress interface-trap formation. By confining plasma
exposure to the gate region, this method mitigates surface degradation
and charge trapping typically observed with CF4 processing,
achieving precise and stable V
th control
without deep gate recessing. The fabricated devices exhibit normally
off operation while maintaining low gate leakage under bias stress.
This single step, lithographically confined approach offers a practical
route toward E-mode GaN HEMTs for energy-efficient, high-frequency,
and high-power electronic systems.