Defect-Mediated Threshold Voltage Tuning in β-Ga₂O₃ MOSFETs via Fluorine Plasma Treatment

Area of Science:

• Wide-bandgap semiconductor research
• Gallium oxide (Ga₂O₃) power electronics
• Plasma-based surface modification

Background:

• β-Ga₂O₃ is a promising material for next-generation power electronics due to its superior properties.
• Surface states and defects in β-Ga₂O₃ limit device performance, particularly off-state leakage and breakdown voltage.
• Plasma-assisted molecular beam epitaxy (PA-MBE) is a key technique for growing high-quality β-Ga₂O₃ epilayers.

Purpose of the Study:

• To investigate the effect of fluorine (F) incorporation via CF₄-plasma treatment on β-Ga₂O₃ MOSFETs.
• To suppress donor-like surface states and improve device performance metrics such as off-state current and breakdown voltage.
• To achieve controllable threshold voltage engineering in β-Ga₂O₃ power devices.

Main Methods:

• Growth of β-Ga₂O₃ epilayers using plasma-assisted molecular beam epitaxy (PA-MBE).
• Optimization of CF₄-plasma treatment to introduce fluorine into the near-surface region.
• Device fabrication and characterization of MOSFETs, including electrical measurements and X-ray photoelectron spectroscopy (XPS).
• Sentaurus TCAD simulations for physical modeling of device behavior.

Main Results:

• High crystalline quality β-Ga₂O₃ epilayers confirmed by XRD and AFM.
• Optimized CF₄-plasma treatment effectively suppressed donor-like states, leading to ultralow off-state current (1 × 10^-9 mA/mm) and a high on/off ratio (10⁵).
• Controllable positive threshold voltage shift up to +12.4 V achieved by adjusting plasma duration.
• Breakdown voltage increased from 453 V to 859 V, attributed to reduced near-surface charge and a widened depletion region.
• XPS analysis confirmed F-Ga bond formation and compensation of oxygen-related donor defects.

Conclusions:

• Fluorine incorporation is an effective strategy for passivating surface states in PA-MBE grown β-Ga₂O₃.
• CF₄-plasma treatment enables significant improvements in leakage suppression and breakdown voltage for Ga₂O₃ power devices.
• This work provides a clear understanding of fluorine's role in defect modulation and demonstrates a viable method for threshold voltage engineering.