Fundamentals of Metal Contact to p-Type GaN—A New Multilayer Energy-Saving Design

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

TITLE: Fundamentals of the Metal Contact to p-type GaN— New Multilayer Energy Saving Design

In this work the authors propose a new type of the contact, which it is created employing multiple layer implantation of the deep acceptors. Where the development of such contact will remove one of the main obstacles in the development of highly efficient nitride optoelectronic devices, both LEDs and LDs: energy loss and the excessive heat production close to the multiple quantum wells system. However, the following comments could help improve the manuscript.

 

1. CORRECT ABSTRACT
2. INTRODUCTION
3. a) In the introduction at the end of line 78, the authors should broadly describe the objective of the research work, as well as its development, highlighting the advantages that the new type of contact presents.
4. THE MODEL
5. a) In line 88, place the acronym 𝐸_𝑏𝑎𝑟, after presenting its definition.
6. b) On line 93, where Figure 1 is cited, it seems to me that Figure 1 is not cited, only presented.
7. c) In Figure 1, please include the values of the Fermi levels in the metal (Au) and GaN, as well as their difference DV in clause (a).
8. d) In line 105, replace network with lattice, as well as in the rest of the text if you use the term again, and avoid using the word "In addition" so often in the same paragraph.
9. CALCULATION PROCEDURE
10. a) In line 133 mention that the lattice parameters are for a hexagonal GaN structure, just as it is mentioned that in the case of Au it is a cubic structure.
11. 4. THE CALCULATION RESULTS

4.1. DOPING IN THE GaN BULK

• a) In line 151 to present Figure 2, it is not very clear whether the Fermi level and hole concentration correspond to the In-rich InGaN layer?
• CONCLUSIONS
• a) Please rewrite the conclusion, as it contains many clauses. Include a paragraph that highlights the most important aspects of the research in a very specific manner.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Improve the quality of the English language

Author Response

Response to Referees criticism

Reviewer comments are in standard text, our response are in italics

 

Open Review #1

1. CORRECT ABSTRACT

Agreed, the abstract is corrected.

 

2. INTRODUCTION
3. a) In the introduction at the end of line 78, the authors should broadly describe the objective of the research work, as well as its development, highlighting the advantages that the new type of contact presents.

Agreed, we added appropriate paragraph.

 

4. THE MODEL
5. a) In line 88, place the acronym ????, after presenting its definition.

Agreed, the acronym is added.

 

6. b) On line 93, where Figure 1 is cited, it seems to me that Figure 1 is not cited, only presented.

Correct, it was missing. It is added now.

 

7. c) In Figure 1, please include the values of the Fermi levels in the metal (Au) and GaN, as well as their difference DV in clause (a).

The values are added now.

 

8. d) In line 105, replace network with lattice, as well as in the rest of the text if you use the term again, and avoid using the word "In addition" so often in the same paragraph.

There was single word “network’. It is incorrect so it was replaced by lattice now. And right there were many ‘in addition’ in the text. Most is removed now.

 

9. CALCULATION PROCEDURE
10. a) In line 133 mention that the lattice parameters are for a hexagonal GaN structure, just as it is mentioned that in the case of Au it is a cubic structure.

Right, it is added now.

 

11. THE CALCULATION RESULTS

4.1. DOPING IN THE GaN BULK

• a) In line 151 to present Figure 2, it is not very clear whether the Fermi level and hole concentration correspond to the In-rich InGaN layer?

No, this is simplest version for pure GaN. It is added now.

 

• CONCLUSIONS
• a) Please rewrite the conclusion, as it contains many clauses. Include a paragraph that highlights the most important aspects of the research in a very specific manner.

Actually we prefer the way it is. Surely, it is specific. The conclusions are designed to prove that the paper changes the state of the art, i.e. it is worth publishing. It is easy to see that the paper provides the important and new data so they change something. There are many papers contributing nothing, this is the way to avoid that. All we could say that in the future reviews we will propose all papers to follow this scheme.

 

Open Review 2

 

1. There is no place in the text that explicitly calls Figure 1.

Correct it was not, it is added now.

 

2. After Fig. 4, the figure numbers jump to Fig. 6. Apparently Figs. 6, 7, 8, 9 should have their figure numbers reduced by 1.

This is obvious error and we apologize for that. The figures are renumbered now.

 

Open Review 3

• Normally p-type GaN annealing will be done in nitrogen ambient. But Author chosen oxygen? Could you explain it.

These are two different, separate processes. The first is to remove hydrogen from MOVPE layers and activate p-type. For MBE layers is not used. Hydrogen escapes across GaN(0001) free surface. In presence of nitrogen Mg is not acceptor. The process was originally discovered by Amano & Akasaki as electron irradiation and then finally discovered as annealing by Nakamura. The oxygen is harmful to this process. This process is not discussed.

The second is oxygen atmosphere annealing of Ni-Au contact after deposition of layered structure. Ni diffuses across Au layer, but oxygen cannot penetrate in the opposite direction. On top nickel oxide is formed so the process is continued. This is most likely the use of oxygen. The second process is in lower temperature. This process is discussed in the paper.

 

• Why didn’t the author mention any carrier transport mechanism (i.e. thermionic emission or thermionic-field emission or Field emission) for their study.

This was not calculated. The carrier may jump due to thermal excitation above the barrier or due to quantum overlap which is essentially tunneling. The second depends on the density of the defects, and the extension of their wavefunctions, the first is related to the depth of the level. This may be obtained from these data, but essentially, these energies are still under discussion, so the number will require careful studies. This is beyond the scope of the paper.

 

• Why didn’t the author consider density of states at the metal-semiconductor interfaces.

For semiconductor DOS is included in the density of holes which is DOS multiplied by occupation probability. In the metal the density of electron is high, due to DOS and partial occupation of the entire band,  this was used to neglect the penetration depth in the metal.

 

• Author should remove ‘¸’ and replaced by ‘to’.

OK, we has verified that.

 

We apologize for the errors and we thank all Referees for their careful reading of the manuscript and help to improve the manuscript considerably. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The need for an ohmic contact on p-type GaN is an important problem, which the authors are addressing. The metal-semiconductor interface is modeled in detail. Characteristics of the band profiles and other parameters are modeled as functions of doping and the degree of acceptor-donor compensation. It is concluded that single-step tunneling will not be a viable way of making a low resistance contact. As a new solution, the authors propose forming the contact with a series of layers, each containing a different dopant that together form a chain of localized levels that will make a current path in a series of tunneling steps. The analysis is good and it is thorough.

This will be a good paper, but some corrections are necessary before this manuscript can be published.

1. There is no place in the text that explicitly calls Figure 1.
2. After Fig. 4, the figure numbers jump to Fig. 6. Apparently Figs. 6, 7, 8, 9 should have their figure numbers reduced by 1.

Comments on the Quality of English Language

The English grammar needs improvement. The authors should have this manuscript edited by someone who is very experienced at writing English.

Author Response

Response to Referees criticism

Reviewer comments are in standard text, our response are in italics

 

Open Review #1

1. CORRECT ABSTRACT

Agreed, the abstract is corrected.

 

2. INTRODUCTION
3. a) In the introduction at the end of line 78, the authors should broadly describe the objective of the research work, as well as its development, highlighting the advantages that the new type of contact presents.

Agreed, we added appropriate paragraph.

 

4. THE MODEL
5. a) In line 88, place the acronym ????, after presenting its definition.

Agreed, the acronym is added.

 

6. b) On line 93, where Figure 1 is cited, it seems to me that Figure 1 is not cited, only presented.

Correct, it was missing. It is added now.

 

7. c) In Figure 1, please include the values of the Fermi levels in the metal (Au) and GaN, as well as their difference DV in clause (a).

The values are added now.

 

8. d) In line 105, replace network with lattice, as well as in the rest of the text if you use the term again, and avoid using the word "In addition" so often in the same paragraph.

There was single word “network’. It is incorrect so it was replaced by lattice now. And right there were many ‘in addition’ in the text. Most is removed now.

 

9. CALCULATION PROCEDURE
10. a) In line 133 mention that the lattice parameters are for a hexagonal GaN structure, just as it is mentioned that in the case of Au it is a cubic structure.

Right, it is added now.

 

11. THE CALCULATION RESULTS

4.1. DOPING IN THE GaN BULK

• a) In line 151 to present Figure 2, it is not very clear whether the Fermi level and hole concentration correspond to the In-rich InGaN layer?

No, this is simplest version for pure GaN. It is added now.

 

• CONCLUSIONS
• a) Please rewrite the conclusion, as it contains many clauses. Include a paragraph that highlights the most important aspects of the research in a very specific manner.

Actually we prefer the way it is. Surely, it is specific. The conclusions are designed to prove that the paper changes the state of the art, i.e. it is worth publishing. It is easy to see that the paper provides the important and new data so they change something. There are many papers contributing nothing, this is the way to avoid that. All we could say that in the future reviews we will propose all papers to follow this scheme.

 

Open Review 2

 

1. There is no place in the text that explicitly calls Figure 1.

Correct it was not, it is added now.

 

2. After Fig. 4, the figure numbers jump to Fig. 6. Apparently Figs. 6, 7, 8, 9 should have their figure numbers reduced by 1.

This is obvious error and we apologize for that. The figures are renumbered now.

 

Open Review 3

• Normally p-type GaN annealing will be done in nitrogen ambient. But Author chosen oxygen? Could you explain it.

These are two different, separate processes. The first is to remove hydrogen from MOVPE layers and activate p-type. For MBE layers is not used. Hydrogen escapes across GaN(0001) free surface. In presence of nitrogen Mg is not acceptor. The process was originally discovered by Amano & Akasaki as electron irradiation and then finally discovered as annealing by Nakamura. The oxygen is harmful to this process. This process is not discussed.

The second is oxygen atmosphere annealing of Ni-Au contact after deposition of layered structure. Ni diffuses across Au layer, but oxygen cannot penetrate in the opposite direction. On top nickel oxide is formed so the process is continued. This is most likely the use of oxygen. The second process is in lower temperature. This process is discussed in the paper.

 

• Why didn’t the author mention any carrier transport mechanism (i.e. thermionic emission or thermionic-field emission or Field emission) for their study.

This was not calculated. The carrier may jump due to thermal excitation above the barrier or due to quantum overlap which is essentially tunneling. The second depends on the density of the defects, and the extension of their wavefunctions, the first is related to the depth of the level. This may be obtained from these data, but essentially, these energies are still under discussion, so the number will require careful studies. This is beyond the scope of the paper.

 

• Why didn’t the author consider density of states at the metal-semiconductor interfaces.

For semiconductor DOS is included in the density of holes which is DOS multiplied by occupation probability. In the metal the density of electron is high, due to DOS and partial occupation of the entire band,  this was used to neglect the penetration depth in the metal.

 

• Author should remove ‘¸’ and replaced by ‘to’.

OK, we has verified that.

 

We apologize for the errors and we thank all Referees for their careful reading of the manuscript and help to improve the manuscript considerably. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Report #1:

In this work, Sakowski et al. studied fundamentals of the metal contact to p-type GaN. This work is important in new multilayer energy saving design for semiconductor devices. I recommend the manuscript to publish after the following comments are addressed:

• Normally p-type GaN annealing will be done in nitrogen ambient. But Author chosen oxygen? Could you explain it.
• Why didn’t the author mention any carrier transport mechanism (i.e. thermionic emission or thermionic-field emission or Field emission) for their study.
• Why didn’t the author consider density of states at the metal-semiconductor interfaces.
• Author should remove ‘¸’ and replaced by ‘to’.

Author Response

Response to Referees criticism

Reviewer comments are in standard text, our response are in italics

 

Open Review #1

1. CORRECT ABSTRACT

Agreed, the abstract is corrected.

 

2. INTRODUCTION
3. a) In the introduction at the end of line 78, the authors should broadly describe the objective of the research work, as well as its development, highlighting the advantages that the new type of contact presents.

Agreed, we added appropriate paragraph.

 

4. THE MODEL
5. a) In line 88, place the acronym ????, after presenting its definition.

Agreed, the acronym is added.

 

6. b) On line 93, where Figure 1 is cited, it seems to me that Figure 1 is not cited, only presented.

Correct, it was missing. It is added now.

 

7. c) In Figure 1, please include the values of the Fermi levels in the metal (Au) and GaN, as well as their difference DV in clause (a).

The values are added now.

 

8. d) In line 105, replace network with lattice, as well as in the rest of the text if you use the term again, and avoid using the word "In addition" so often in the same paragraph.

There was single word “network’. It is incorrect so it was replaced by lattice now. And right there were many ‘in addition’ in the text. Most is removed now.

 

9. CALCULATION PROCEDURE
10. a) In line 133 mention that the lattice parameters are for a hexagonal GaN structure, just as it is mentioned that in the case of Au it is a cubic structure.

Right, it is added now.

 

11. THE CALCULATION RESULTS

4.1. DOPING IN THE GaN BULK

• a) In line 151 to present Figure 2, it is not very clear whether the Fermi level and hole concentration correspond to the In-rich InGaN layer?

No, this is simplest version for pure GaN. It is added now.

 

• CONCLUSIONS
• a) Please rewrite the conclusion, as it contains many clauses. Include a paragraph that highlights the most important aspects of the research in a very specific manner.

Actually we prefer the way it is. Surely, it is specific. The conclusions are designed to prove that the paper changes the state of the art, i.e. it is worth publishing. It is easy to see that the paper provides the important and new data so they change something. There are many papers contributing nothing, this is the way to avoid that. All we could say that in the future reviews we will propose all papers to follow this scheme.

 

Open Review 2

 

1. There is no place in the text that explicitly calls Figure 1.

Correct it was not, it is added now.

 

2. After Fig. 4, the figure numbers jump to Fig. 6. Apparently Figs. 6, 7, 8, 9 should have their figure numbers reduced by 1.

This is obvious error and we apologize for that. The figures are renumbered now.

 

Open Review 3

• Normally p-type GaN annealing will be done in nitrogen ambient. But Author chosen oxygen? Could you explain it.

These are two different, separate processes. The first is to remove hydrogen from MOVPE layers and activate p-type. For MBE layers is not used. Hydrogen escapes across GaN(0001) free surface. In presence of nitrogen Mg is not acceptor. The process was originally discovered by Amano & Akasaki as electron irradiation and then finally discovered as annealing by Nakamura. The oxygen is harmful to this process. This process is not discussed.

The second is oxygen atmosphere annealing of Ni-Au contact after deposition of layered structure. Ni diffuses across Au layer, but oxygen cannot penetrate in the opposite direction. On top nickel oxide is formed so the process is continued. This is most likely the use of oxygen. The second process is in lower temperature. This process is discussed in the paper.

 

• Why didn’t the author mention any carrier transport mechanism (i.e. thermionic emission or thermionic-field emission or Field emission) for their study.

This was not calculated. The carrier may jump due to thermal excitation above the barrier or due to quantum overlap which is essentially tunneling. The second depends on the density of the defects, and the extension of their wavefunctions, the first is related to the depth of the level. This may be obtained from these data, but essentially, these energies are still under discussion, so the number will require careful studies. This is beyond the scope of the paper.

 

• Why didn’t the author consider density of states at the metal-semiconductor interfaces.

For semiconductor DOS is included in the density of holes which is DOS multiplied by occupation probability. In the metal the density of electron is high, due to DOS and partial occupation of the entire band,  this was used to neglect the penetration depth in the metal.

 

• Author should remove ‘¸’ and replaced by ‘to’.

OK, we has verified that.

 

We apologize for the errors and we thank all Referees for their careful reading of the manuscript and help to improve the manuscript considerably. 

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Author answered to my questions.