Electrical Characteristics of Diamond MOSFET with 2DHG on a Heteroepitaxial Diamond Substrate

Round 1

Reviewer 1 Report

The paper is worth publishing. It is an experimental work that can contribute to the state of the art. However, I would like to suggest some additions to help the reader understand the physics behind the device operation, without the need for an extensive search. The authors may consider the following issues if the editor agrees:

• Since this is a normally-on device, it is assumed that there is a conducting channel under the gate. Explain how this hole-channel is formed? A simple explanation would be enough.
• Since this is an interface device, it would help the reader to see an energy band diagram for the device. Is there a quantum well at the interface due to surface band bending? How does the band look?
• The dielectric is grown using ALD, which is assumed to grow materials with low defect densities. Why are there 1.66 a10¹³/cm² and trapped charges of 4.03 x 10¹² /cm³ these are very high values for the device to be stable? Can you explain?
• Any evidence for the validity of the explanation for the decrease of the negative charges with annealing?
• Any evidence for the validity of the explanation for the increase of mobility and the subsequent decrease with annealing?

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents original results on the fabrication of diamond MOSFET on a free-standing heteroepitaxial single crystal diamond. The results are meaningful and clearly presented. The following points should be addressed before publication: 

1) The language in the introduction is sometimes vague: "It is gratifying that diamond heteroepitaxy on Ir has achieved some excellent results" - It is not clear what is meant by excellent results. When say "China has achieved excellent results". 

The same applies to the sentence: "The performance of MOSFET with the same size is much better than that we reported previously". It is not clear what is meant by "the performance".

2) Materials and methods sections start with the results of XRD (first sentence) obtained by characterization of the diamond sample, and photographs of the diamond sample(second sentence). The description of sample preparation is after the results. 

I recommend following chronological order - first to write how was the sample preparation and after that how it was characterized. Otherwise, it is confusing for readers. 

3) The substrate for diamond growth is not specified. 

4) Type of MPCVD system is not mentioned. 

5) The conclusion states "The annealing condition for Al2O3/H-diamond need to be controlled precisely." It is not clear what is meant by precise control.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Paper title: Electrical characteristics of diamond MOSFET with 2DHG on heteroepitaxy diamond substrate 

Paper ID: materials-1627638

Semiconducting diamond has become recently an important material for manufacturing various kinds of electron devices, including  high-energy particle detectors and MOSFETs resistant to nuclear radiation or high temperatures. The paper is of interest, since the authors  show the possibility of making a MOSFET with the channel in a an epitaxial layer of  hydrogen-terminated diamond grown on the substrate fabricated from heteroepitaxial single crystal diamond. However, in the presentation of results there are many points that need to be clarified and improved.

1. The authors give just a FWHM value of the substrate rocking curve obtained by X-ray measurements. A comment concerning the crystallographic quality of the substrate material  is needed. Comparison with the rocking curve characteristics for other materials, e.g. 4H-SiC would be valuable.
2. The two-dimensional hole gas (2DHG) that is mentioned in the title is later on only once mentioned in the introduction. A comment saying how the 2DHG is formed in the H-diamond layer is needed. In particular, the band diagram for the interface between the oxide and the diamond layer should be presented. There is no evidence in the text that the 2DHG can be formed. The low mobility of holes is in the contradiction to the fact the MOSFET is with 2DHG.
3. A comment on the reasons for existing the negative charge in the oxide layer is needed. Please explain why a high density of this charge is observed. What factors can affect the trapped charge density? The dependence of the density of states at the interface on the annealing temperature is strange and should be discussed. With what accuracy is the hole mobility determined. What are the factors influencing the accuracy (uncertainty).
4. Why the current density is given in the units of [mA/mm], not in [mA/mm²] and transconductance in [mS/mm], not in [mS]. Is it somehow normalized? The power density is also in [W/mm], not in [W/mm²]. On page 3, the on-resistance is in [Ωmm], not in [Ω]?
5. On page 2, there is L_SG and L_SD are 9 µm. Should be L_SG and L_GD are 9 µm. Besides, there are a lot of language errors. For example, in the title: there is heteroepitaxy; should be heteroepitaxial, first line of the introduction: there is diamond semiconductor have been studied; should be diamond semiconductor has been studied; first line of second paragraph: there is vast majority, should be the vast majority. Please check thoroughly  the text  in terms of the English and remove the errors related to grammar and style. 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The revised version should be clear for readers.