Positive and Negative Symmetric Pulses with Fast Rising Edge Generated from a GaAs Photoconductive Semiconductor Switch
Round 1
Reviewer 1 Report
My suggestions for the authors are the following:
- Some aspects about the GaAs wafer should be included, such as the wafer thickness and doping level. The values of dark resistance and mobility of GaAs wafer are nominal ones or they were measured on the used wafer?
- What parameters have been used by the authors to design the device? What would be the expected time response of the device with the given geometry?
- Authors should complete the study with other conditions to extract conclusions. Why do they used 2 kV? What happens at both higher/lower bias voltage?
- What is the origin of the obtained time response? The GaAs substrate or the device geometry? How could it be improved?
- Why the fall and rise time are different in a symmetric device?
Author Response
Response to the reviewer 1 Comments for Paper applsci-404278
“Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch”
We really appreciate your effort in carefully reviewing our manuscript entitled " Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch"(ID: applsci-404278).
We are grateful for assessing the manuscript interesting for Applied Science and for the constructive criticisms, comments and suggestions. We considered all issues brought up by the reviewers thoroughly and revised the manuscript accordingly as described below. We believe that by the revisions the paper gained significantly in scientific depth and therefore is well suited for the readership of Applied Science.
Response to reviewer#1:
We would like to express our sincere thanks to you for the constructive and positive comments, and all my responses to the comments are as follows:
Point 1: Some aspects about the GaAs wafer should be included, such as the wafer thickness and doping level. The values of dark resistance and mobility of GaAs wafer are nominal ones or they were measured on the used wafer?
Response 1: Thank you for your suggestion. In our device, the dark resistance of the GaAs is larger than 5 × 107 Ω•cm, and the electron mobility is higher than 5000 cm2 /(V•s), there are all nominal ones. These parameters have been described in the revised manuscript.
Point 2: What parameters have been used by the authors to design the device? What would be the expected time response of the device with the given geometry?
Response 2: Our device is mainly used in a streak camera, the application requires a positive and negative symmetric pulses with fast rising edge with 2kV bias voltage, the photoelectric response time of the GaAs substrate have been used to design the device. In this situation, the rise time of the pulse should be less than 200ps, indeed, it did.
Point 3: Authors should complete the study with other conditions to extract conclusions. Why do they used 2 kV? What happens at both higher/lower bias voltage?
Response 3: Our device was designed for a streak camera, and the streak camera needs the device to work at 2kV bias voltage. Actually, we have measured the output waveforms with higher or lower bias voltage. As shown below.
Fig 1. The output waveform at different bias voltage and 97.5 μJ laser pulse energy. (a) 1.7kV,(b)1.9kV,(c)2.0kV,(d)2.1kV,(e)2.3kV,and(f)2.5kV.
As shown in the graph, the output waveforms are symmetric at bias voltage below 2.3kV. Whereas, when the bias voltage is 2.5kV, the output pulse became asymmetric, and the device operated in the transition stage from linear mode to non-liner mode, with which the lifetime of the device will be shortened.
Point 1: What is the origin of the obtained time response? The GaAs substrate or the device geometry? How could it be improved?
Response 4: The rise time of the pulse is mainly decided by the photoelectric response time of the GaAs substrate, the rise time and pulse width of pump laser. The photoelectric response time of the GaAs material is less than 1ps. The fall time and pulse width of the pulse is mainly decided by the lifetime of carriers of GaAs substrate at a certain the rise time and pulse width of pump laser. Moreover, the performance of the device can be improved through optimizing device geometry parameters. For example, the impedance of device elements should be matched by optimizing the microstrip line.
Point 5: Why the fall and rise time are different in a symmetric device?
Response 5: In our paper, the rise time of positive pulse and the fall time of negative pulse were 174ps and 164ps, and the difference is about 10ps, which is within the error range. The error mainly caused by the electrical elements (resistors and capacitors) in the electronic circuits, because there are random errors between the nominal value and the actual parameters in the symmetric bilateral sweep circuits in Fig. 2 (b).
Fig. 2 (b) The photo of the sweep circuit
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript reports on the time response of a GaAs photoconductive semiconductor switch. The main results (fast rise time, negligible jitter, high stability) are obtained thanks to a sweep circuit, which is the main author contribution and, possibly, to the low jitter time of the used femtosecond laser. Notable performance, better than state of art, has been achieved mainly by designing a simple passive sweep circuit. In view of such results, the manuscript should provide a better insight about the reasons of such success in comparison with previous works. In its present form, the potential impact of this manuscript appearing on Applied Science, is pretty low. Moreover, because the subject, the kind of contribution and the results, the manuscript better fits a more technical, electronic device oriented, journal. Again, this is not a criticism to the content, which can be of high interest for a specialized audience.
Author Response
Response to the reviewer 2 Comments for Paper applsci-404278
“Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch”
We really appreciate your effort in carefully reviewing our manuscript entitled " Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch"(ID: applsci-404278).
We are grateful for assessing the manuscript interesting for Applied Science and for the constructive criticisms, comments and suggestions. We considered all issues brought up by the reviewers thoroughly and revised the manuscript accordingly as described below. We believe that by the revisions the paper gained significantly in scientific depth and therefore is well suited for the readership of Applied Science.
Response to reviewer#2:
We would like to express our sincere thanks to you for the constructive and positive comments, and all my responses to the comments are as follows:
Point: The manuscript reports on the time response of a GaAs photoconductive semiconductor switch. The main results (fast rise time, negligible jitter, high stability) are obtained thanks to a sweep circuit, which is the main author contribution and, possibly, to the low jitter time of the used femtosecond laser. Notable performance, better than state of art, has been achieved mainly by designing a simple passive sweep circuit. In view of such results, the manuscript should provide a better insight about the reasons of such success in comparison with previous works. In its present form, the potential impact of this manuscript appearing on Applied Science, is pretty low. Moreover, because the subject, the kind of contribution and the results, the manuscript better fits a more technical, electronic device oriented, journal. Again, this is not a criticism to the content, which can be of high interest for a specialized audience.
Response: We would like to express our sincere thanks to you for the constructive and positive comments. In this paper, the device is mainly used in streak camera, however, it can also be applied to other applied engineering fields such as precise synchronization control system, ultra-wideband (UWB) microwave radiation, and so on, which we are sure the journal audience out there may be interested in as well.
The manuscript has been improved based on your suggestions
(1)To make clear indication of the motivation, the introduction is revised in the revised manuscript.
Line 25-30
The GaAs PCSSs also have been widely used in THz fields as emitter and detector. When femtosecond laser pulses are focused on the gap of GaAs PCSSs, photo-excited carries generate at the semiconductor’s conduction band, and are subsequently accelerated by the bias electrical field, and terahertz waves radiated at the same time [8-10].
References
8. D. H. Auston. Picosecond optoelectronic switching and gating in silicon. Appl. Phys. Lett. 1975, 26,101, DOI: 10.1063/1.88079.
9. P. R. Smith, D. H. Auston, M. C. Nuss. Subpicosecond photoconducting dipole antennas. IEEE Journal of Quantum Electronics. 1988, 24(2), 255-260, DOI: 10.1109/3.121.
10. Schmuttenmaer C. A. Exploring Dynamics in the Far-Infrared with Terahertz Spectroscopy. Chemical Reviews.2004, 104(4), 1759-1779, DOI: 10.1021/cr020685g
(2)The photo of the sweep circuit, as shown in the fig 2.(b), has been added in our revised manuscript, to make the readers understand our design clearly.
Fig. 2 (b) The photo of the sweep circuit
(3) The results were further analyzed.
The difference between the fall and rise time in a symmetric device is explained. Moreover, a brief description of how to optimize the performance in revised manuscript as given as follows.
Line 79-87
The rise time of positive pulse and the fall time of negative pulse were 174ps and 164ps, and the difference is about 10ps, which is within error range. The error mainly caused by the electrical elements (resistors and capacitors) in electronic circuits, because their values are not exactly same for two corresponding elements in the symmetric sweep circuits in Figure 2. The rise time of the pulse is mainly decided by the photoelectric response time of the GaAs substrate and the time duration of pump laser, the pulse width is mainly decided by the lifetime of carriers of GaAs substrate. Moreover, the performance of the device can be improved through optimizing device geometry parameters. For example, the impedance of device elements should be matched by optimizing the microstrip line.
Author Response File: Author Response.pdf
Reviewer 3 Report
- Overall the paper is well written and presented
- Fig.2 - Show where and how the bias of 2kV is applied to the PCSS
- Fig 3 - indicate the exact terminals (relating fig 2) across which the oscilloscope is connected.
- Will be good to include a picture of the actual hardware (circuit) with the passive components along with the measured results in fig 4 or fig 5
- Add reference "Ultrafast Rising of Input Electric Impulse of High Gain Semi-insulated GaAs PCSS, 2011"
- Pg1, line 39 has a typo should read "rounded corner"
Author Response
Response to the reviewer 3 Comments for Paper applsci-404278
“Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch”
We really appreciate your effort in carefully reviewing our manuscript entitled " Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch"(ID: applsci-404278).
We are grateful for assessing the manuscript interesting for Applied Science and for the constructive criticisms, comments and suggestions. We considered all issues brought up by the reviewers thoroughly and revised the manuscript accordingly as described below. We believe that by the revisions the paper gained significantly in scientific depth and therefore is well suited for the readership of Applied Science.
Response to reviewer#3:
We would like to express our sincere thanks to you for the constructive and positive comments, and all my responses to the comments are as follows:
Point 1: Fig.2 - Show where and how the bias of 2kV is applied to the PCSS
Response 1: As shown in the Fig. 2 (b) in the revised manuscript, the high voltage supply is connected to the sweep circuit by the high voltage transmission line.
Fig. 2 (b) The photo of the sweep circuit
Point 2: Fig 3 - indicate the exact terminals (relating fig 2) across which the oscilloscope is connected.
Response 2: As shown in the Fig. 2 (b) and Fig. 3 in the revised manuscript, the sweep circuit is connected with a 50W coaxial line by SMA. The output voltage is attenuated by a 60-dB attenuator and recorded by an oscilloscope.
Fig. 3 Schematic diagram of testing circuit
Point 3: Will be good to include a picture of the actual hardware (circuit) with the passive components along with the measured results in fig 4 or fig 5
Response 3: Thank you for your suggestion, and the physical map of the sweep circuit has been added in our revised manuscript, as shown in the fig 2.(b).
Point 4: Add reference "Ultrafast Rising of Input Electric Impulse of High Gain Semi-insulated GaAs PCSS, 2011"
Response 4: We apologize for this negligence, the reference" Ji W , Shi W , Jia W . Ultrafast rising of output electric impulse of high gain semi-insulated GaAs PCSS. Proceedings of 2011 International Conference on Electronics and Optoelectronics, Dalian, Liaoning, China, 2011.07.29-2011.07.31; 2011:V3284-V3286. "has been added in our revised manuscript.
Point 5: Pg1, line 39 has a typo should read "rounded corner"
Response 5: We are very sorry for this mistake, and we have made correction in our revised manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Before publishing in Applied Science I strongly suggest the following points:
1.- The selection of the device geometry and dimensions is still an open question and the authors do not explain it.
2.- The explanation concerning the difference between rise and fall time should be included in the text, as it is addressed to the error bar but given numerically without error bar in the abstract.
Author Response
Response to the reviewer 1 Comments for Paper applsci-404278
“Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch”
We really appreciate your effort in carefully reviewing our manuscript entitled " Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch"(ID: applsci-404278).
We are grateful for assessing the manuscript interesting for Applied Science and for the constructive criticisms, comments and suggestions. We considered all issues brought up by the reviewers thoroughly and revised the manuscript accordingly as described below. We believe that by the revisions the paper gained significantly in scientific depth and therefore is well suited for the readership of Applied Science.
Response to reviewer#1:
We would like to express our sincere thanks to you for the constructive and positive comments, and all my responses to the comments are as follows:
Point 1: The selection of the device geometry and dimensions is still an open question and the authors do not explain it.
Response 1: In our paper, the individual components in Figure 1 are described in more detail as follows.
To meet the requirement of a femtosecond streak camera, a sweep circuit was designed, with the core component of a GaAs PCSSs. The schematic diagram of a lateral GaAs PCSSs for the experiment is shown in Figure 1. The bottom copper board is part of the transmission line, the Al2O3 insulation layer is located between the copper board and GaAs substrate. The nominal dark resistance of the GaAs is larger than 5 × 107 Ω•cm, and the electron nominal mobility is higher than 5000 cm2 /(V•s).The two Au/Ge/Ni electrodes form the ohmic contact with GaAs substrate. The size of each electrode is 6 mm × 3 mm, and the electrodes were rounded with the corner radius of 1.1 mm in order to uniform the electric field distribution. The gap between the two electrodes is 3.5 mm. Multi-layer transparent dielectrics used as the passivation and insulation protection materials are deposited and coated on the surface of the GaAs PCSSs. The switch was connected with external circuit using coaxial transmission lines.
Point 2: The explanation concerning the difference between rise and fall time should be included in the text, as it is addressed to the error bar but given numerically without error bar in the abstract.
Response 2:
These explanations (as follows) have been added in our revised manuscript.
The rise time of positive pulse and the fall time of negative pulse were 174ps and 164ps, and the difference is about 10ps, the error is about 6%，which is within the margin of error，for a femtosecond streak camera. The error mainly caused by the
electrical elements (resistors and capacitors) in the electronic circuits, because there are random errors between the nominal value and the actual parameters in the symmetric bilateral sweep circuits in Figure 2.
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors have moderately accounted for the raised criticisms and the manuscript is technically satisfactory. The manuscript can now be published if the editor finds it of interest for the readers of Applied Sciences
Author Response
Response to the reviewer 2 Comments for Paper applsci-404278
“Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch”
We really appreciate your effort in carefully reviewing our manuscript entitled " Positive and negative symmetric pulses with fast rising edge generated from a GaAs photoconductive semiconductor switch"(ID: applsci-404278).
We are grateful for assessing the manuscript interesting for Applied Science and for the constructive criticisms, comments and suggestions. We considered all issues brought up by the reviewers thoroughly and revised the manuscript accordingly. We believe that by the revisions the paper gained significantly in scientific depth and therefore is well suited for the readership of Applied Science.
Response to reviewer#2:
We would like to express our sincere thanks to you for the constructive and positive comments, and all my responses to the comments are as follows:
Point: The authors have moderately accounted for the raised criticisms and the manuscript is technically satisfactory. The manuscript can now be published if the editor finds it of interest for the readers of Applied Sciences
Response: Thank you very much for the positive evaluation to our revised manuscript. Your suggestions and comment is very important to improve the manuscript.
Author Response File: Author Response.pdf
