Increased Mobility in 4H-SiC MOSFETs by Means of Hydrogen Annealing

Round 1

Reviewer 1 Report

The paper proposes an additional step in the fabrication of 4H-SiC MOSFETs by annealing immediately prior to the deposition of the Al2O3 with outstanding results. The topic is a subject of intense debate and the author’s contribution is very clear. However, even though there are many valid measures in the paper, any of those techniques do not help to understand the hypothesis of why improvement by this procedure appears. The author’s explanation is based on references, and those references use some Depth profile techniques such as SIMS, STM, AFM or LEED etc... to understand this phenomenon. Depth profile techniques or maybe a SEM comparing the surface generating by two procedures are necessary for this paper, and it is even more important because is the Crystals journal. 

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Author Response

Please find the response to the reviewer's comment in the attachment. Thank you.

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript, the authors demonstrated the use of forming gas anneal to achieve an improved Al2O3-SiC interface which can benefit the field effect mobility in enhancement mode SiC MOSFETs. 

The materials and methods section lacks comprehensive information and needs to be revised. Please give more information about the 4H-SiC substrates used including supplier. A diagram showing the fabrication process and the final SiC MOSFET must be included. The following process information is missing: ion-implant energy, implanted ion for the source and drain, the photolithography and alignment process and the thickness measurement of the Al2O3 and SiO2.  The C-psi method for extracting the Dit should be explained in more detail. 

In section 3, the authors only presented the results which are valid but there is no discussion. The results need to be properly and fully interpreted. In the Id-Vgs characteristic, explain why there is a large difference in the extracted Vth and subthreshold slope between the forming gas annealed device and the control. What extraction method was used to find the Vth? Arrows need to be added to fig. 1 to show the forward sweep and backward sweep of the voltage. For the control sample, there is hysteresis both below and above Vth. Therefore, it is not convincing to argue that the hysteresis above Vth is due to Al2O3 only. Please add a reference to support this assertion and clarify. 

Fig. 4 has the same clarity issue. What method was used to extract the field effect mobility of both devices. Why is there a maximum in the field effect mobility near the threshold voltage of the device annealed in forming gas? Since the much higher field effect mobility is related to the surface defects, there should be a more in-depth discussion of the ON1/ON2 defects. It is also necessary to clarify how hydrogen can etch SiC. 

For the threshold voltage measurement in fig. 5, is there any more change in the Vth after the fourth measurement? This is because threshold stability is important for power converter circuits. 

Authors should also correct some typographic errors in the manuscript. There are undefined symbols Ec, E, C and psi in section 1. The first 'galium' in line 13 should be corrected. There is another error in the inequality sign in line 83. 

 

Author Response

Please find the response to the reviewer's comment in the attachment. Thank you.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The improvements in this version are evident. One minor remark about the resolution of Figure 1. Congratulations on your contribution.