Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This article focus on the fabrication and characterization of quasi-vertical GaN-based trench gate MOSFETs treated with fluorine plasma, demonstrating a significant improvement in breakdown voltage from 100 V to 275 V through F-plasma treatment, This is ascribed to reduced peak electric field at the gate edge. This sounds interesting, but suffers from significant insufficiencies, including inconsistent data presentation, insufficient experimental characterization, lack of quantitative comparisons with state-of-the-art, and inadequate physical explanation of the results. The authors need to address  the following issues, before the manuscript can be accepted for publication.

Comment 1 

 The manuscript lacks critical experimental details necessary for reproducibility and scientific validation, including:Gate dielectric quality: The ALD Al₂O₃ gate dielectric is mentioned, but there is no C-V characterization, no capacitance-equivalent thickness (CET) data, and no breakdown field strength of the dielectric itself.  Ohmic contact characterization: The manuscript states that Ti/Al/Ni/Au was used for source/drain ohmic contacts, but no specific contact resistance values or annealing conditions are provided. What is the specific contact resistivity achieved? F-plasma profile: No SIMS or XPS data are provided to confirm fluorine incorporation, its concentration, or its spatial distribution within the device structure. Without this, the "fixed negative charges" mechanism remains speculative.

Comment 2: The abstract point that the breakdown voltage increases from 100 V to 275 V, but in Section 3, it reports that "traditional device A" (gate-in-the-middle without F-plasma) achieves 170 V, while "traditional device B" (gate-on-both-sides without F-plasma) achieves only 100 V. The comparison in the abstract (100 V to 275 V) appears to compare the worst-case untreated device (device B) with the F-plasma treated device, rather than comparing devices with identical structures. This is misleading.

Comment3 The authors regard  the reduction of the peak electric field via fixed negative charges from F-plasma treatment as the only reason for breakdown voltage improvement. However, Figure 3 shows that the leakage current of the F-plasma treated device at voltages below breakdown is higher than that of the untreated device, which contradicts the "depletion region" explanation. This suggests that additional mechanisms, such as modification of the surface states or changes in the barrier height, may be at play, but these are not discussed.

Comment 4:The manuscript indicate that the system has been achieved a maximum saturation current of 2258.2 A/cm² and an Ron,sp of 7.2 mΩ·cm², but no comparison is made with previously reported quasi-vertical GaN MOSFETs. This is essential to demonstrate the significance of the work. For example, the authors should compare their results with those of Zhu et al. (2022), Ji et al. (2018), and others cited in the introduction.

Comment5：The notation "F- plasma" is inconsistent throughout the manuscript. Please standardize to "F-plasma" or "fluorine plasma."

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a quasi-vertical GaN trench-gate MOSFET incorporating fluorine-plasma treatment to improve the breakdown voltage. The study demonstrates that the proposed treatment increases the breakdown voltage from 100 V to 275 V, and combines electrical characterization, TCAD simulations, and preliminary stress tests to investigate the device behavior. The topic is relevant to GaN power electronics, and the application of fluorine-plasma treatment to a trench-gate MOSFET is of interest. However, the manuscript represents an incremental advance over the authors' previous work on fluorine-treated GaN diodes, and several issues should be addressed before the work is suitable for publication.

(1) The manuscript claims that fluorine-plasma treatment is applied for the first time to quasi-vertical GaN trench MOSFETs. While this may be correct, the underlying mechanism (fluorine-induced negative fixed charge for electric-field redistribution and leakage suppression) has already been established in the authors' previous studies on GaN Schottky and PiN diodes. The manuscript should clearly distinguish what is genuinely new in this work. 

(2) The simulation methodology lacks sufficient detail. Without these details, the simulation results cannot be independently assessed or reproduced.

(3) The manuscript would benefit from a comparison table summarizing key performance metrics (breakdown voltage, specific on-resistance, current density, and threshold voltage) relative to recently reported quasi-vertical and vertical GaN trench MOSFETs.

(4) The manuscript requires thorough English editing. Numerous grammatical errors and inconsistent terminology are present throughout the paper. Professional language editing is recommended.

(5) Figure captions should be revised for clarity. It is unclear based on the current caption whether the figure is a simulation or a measurement based on the DUT. The definitions of "Traditional device A" and "Traditional device B" are not sufficiently intuitive and make the manuscript difficult to follow. The authors should replace these labels with descriptive names.  

 

Comments on the Quality of English Language

The manuscript requires thorough English editing. Numerous grammatical errors and inconsistent terminology are present throughout the paper. Professional language editing is recommended.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf