Messages

1

General Questions and Answers / Re: Boundary condition of device configuration with gate

« on: April 14, 2014, 22:49 »

Thanks very much, Anders.

2

General Questions and Answers / Re: Boundary condition of device configuration with gate

« on: April 14, 2014, 16:26 »

Could someone please give me some help on this problem? Thanks

3

General Questions and Answers / Boundary condition of device configuration with gate

« on: April 6, 2014, 03:06 »

Hello Sir/Madam,

I would like to simulate a FET device made of graphene sheet (Please see the first picture attached).


Q1: when I repeat my device configuration in A&B direction for 2*2 times to check how it looks like, I found the gate is not repeated like the graphene sheet (Please see the second attached picture).

But in this topic: http://quantumwise.com/forum/index.php?topic=2204.0#.U0CjBfldX54 , Anders said the gate should be repeated too. So what is the problem?

Q2: Since the central region is graphene sheet (not graphene nanoribbon, which means there is no bandgap), I used periodic boundary condition for multi-grid poisson solver in the B direction without any additional vacuum area (please see the third attached picture for the whole boundary condition settings), is it correct? Should I use Neumann boundary condition for both A and B direction in this device configuration with a gate?

Thanks in advance and looking forward to your reply.

Regards

4

General Questions and Answers / Re: Self-Consistent and Linear I-V characteristics

« on: April 1, 2014, 01:42 »

I am also willing to know the answer. And by the way, I am adding another question and hopefully I could find the answer here:

In some device configuration with a top (or bottom) gate, we know the gate voltage will shift the transmission spectrum (say for a device with energy gap, it shifts the energy gap window) to left (or right) depends on the polarity of the gate potential.

However, if it possible for a bias voltage applied on the electrodes that shifts the transmission spectrum in the same manner?

It looks to me the answer is no. Is it correct?

Thanks

5

General Questions and Answers / single ended vs differential bias

« on: April 1, 2014, 01:30 »

Hello Sir/Madam,

I noticed in the Tutorials, when we calculate the I-V characteristics of a two electrodes device, differential bias voltage is used in the electrodes. So the question is:

1. Why don't use single ended voltage (by setting the voltage of one electrode to zero) ? Will the simulation results be different with the differential case? Is there going to be any problem when single ended voltage is used (for example self-consistent calculation becomes harder to converge)?

2. If single ended voltage is suitable to do the I-V characteristic calculation, how do we extract the I-V curve from a converged calculation?

Thanks and looking forward to your reply.

6

General Questions and Answers / Re: non-rectangular gate geometry

« on: March 24, 2014, 12:54 »

Thanks. I got it.

But I have another question about the gate geometry.

By using the command Zmin, Zmax, etc. We can draw a rectangular gate easily. However, that also means the sides of the gate should be aligned with the x(or y,z) direction. If it possible to have a rectangular gate with side in any direction (for example align with the line that is (for example 45 degree) between the y,z axis in the yz plane).

Thanks in advance and looking forward to your reply.

7

General Questions and Answers / non-rectangular gate geometry

« on: March 20, 2014, 23:14 »

Hello,

I am wondering if it possible to generate a device with non-rectangular gate shape, for example a triangular one.

It seems in the Builder we can only create a gate with rectangular shape (by setting the minimum and maximum in x, y directions). Is there any other way to determine the geometry of the gate?

Thanks in advance.

Regards

8

General Questions and Answers / Add metal directly on graphene layer

« on: March 13, 2014, 21:03 »

I am wondering how to add metal as a interconnect wire (so it looks like a top gate without dielectric) directly on the top of a graphene layer (not on the sides) in ATK.

I know how to add metal from this example http://quantumwise.com/documents/tutorials/latest/BenzeneSET/index.html/chap.SET.html

But when there is no dielectric between metal and graphene, how much distance should I give between them (metal and graphene)? 1.42A ?

Thanks in advance.

9

General Questions and Answers / Re: Transport calculation direction

« on: December 10, 2013, 19:29 »

Thanks for your reply, Anders.

I have read your paper: doi:10.1103/PhysRevB.85.165442 .

I think the configuration I would like simulate is very similar to the nickel-graphene case (just need to replace the nickel atoms with doped-silicon, and add a vertical gate bias on the interface of nickel and graphene).

If you still do not understand what the configuration is, please have a look at this paper:

[ J. Chauhan, A. Rinzler, and J. Guo, "A Computational Study of Graphene Silicon Contact", J. Appl. Phys., vol. 112, p. 104502, 2012. ]

Download address: http://scitation.aip.org/content/aip/journal/jap/112/10/10.1063/1.4759152

The gated graphene-doped_silicon contact presented in it is exactly what I would like to study with ATK.

I hope all your confusions should be clear in it and I am looking forward to your suggestions.

Best

10

General Questions and Answers / Re: Transport calculation direction

« on: December 5, 2013, 12:18 »

Hello anders,

what do you think about my confusion above?

Looking forward to your reply. Thanks

Best

11

General Questions and Answers / Re: Transport calculation direction

« on: December 3, 2013, 12:05 »

Thanks Anders. I got your idea. Just one more confusion:

Since the aim of my work is to study the electron transport through the schottky barrier (between graphene and "s:doped-silicon") under different bias voltages, which means the electron should transport across the graphene layer.

However, as shown in your configuration:

                                           the left electrode consists of  a thin "e" with thin "s" on top, plus "G"
                                           right electrode includes "G" and thin "e" on the top
                                           central region is filled with graphene

Thus, when we calculate its I-V characteristics, it seems only the electron transport along the graphene layer is taken into consideration. To my understanding, this has no difference with the structure with only graphene in the whole device (please see the picture below)


----------------------> z direction

                          | (gate: bias-voltage) |
                          v                             v     
                           ********************     
                           ****      dielectric     ***                   
                           ********************                  (electrode:source)         
                          GGGGGGGGGGGGGGGGGGGGG  GGGGGGG  GGGGGGGGGGGGGG            /\
                          GGGGGGGGGGGGGGGGGGGGG  GGGGGGG  GGGGGGGGGGGGGG            |
  (electrode:drain)  GGGGGGGGGGGGGGGGGGGGG  GGGGGGG  GGGGGGGGGGGGGG            |
                                                                                                                      |    X direction
                                                              (Central region)

12

General Questions and Answers / Re: Transport calculation direction

« on: December 1, 2013, 18:27 »

Sorry Anders, I guess I didn't make it clear. In fact, I would like to study the effect of bias voltage on the schottky barrier between graphene and doped-silicon (please see the picture below). I would like to simulate the I-V characteristics of this configuration under different bias voltage.


----------------------> x (or y) -direction
                                                                                                                                     
                                                                                                                                                                                                                                                                                                                         
                                     | (gate: bias-voltage) |
                                     v                             v      (electrode:source)
                                   ********************   eeeeeeeeeeeeeeee
                                   ****     dielectric    ****    eeeeeeeeeeeeeeee       
                                   ********************   eeeeeeeeeeeeeeee               
                                  GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG                                          /\
                                  GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG  (G:Graphene)                       |
     (schottky barrier)      GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG                                          |    Z-direction
                                   ssssssssssssssssssssssssss                                                                        |
                                   ssssssssssssssssssssssssss      (s: doped-silicon)                                          |
                                   ssssssssssssssssssssssssss                                                                        |
                                   eeeeeeeeeeeeeeeeeeeeeee
                                   eeeeeeeeeeeeeeeeeeeeeee           
                                   eeeeeeeeeeeeeeeeeeeeeee
                                          (electrode:drain)

13

General Questions and Answers / Re: Transport calculation direction

« on: November 29, 2013, 17:24 »

Dear Anders,

Thanks for your reply. In fact, I would like to use the heterogeneous electrodes configuration because I want to apply bias voltage on the central region (see below), The dielectric will be covered on part of the surface of central region. Can ATK simulate the transport of this configuration?

If so, how should I set the cell size of electrodes, central region and dielectric?

Thanks


----------------------> Z-direction
                                                                                                                                     X-direction
(hhhhhhhhhhhhhhhhhhh)  hhhhhhhhhhhhhhhhhhhhhhh   ********************   <-(bias-voltage)    /\
(hhhhhhhhhhhhhhhhhhh)  hhhhhhhhhhhhhhhhhhhhhhh   ****     dielectric     ****   <-(bias-voltage)    |
(hhhhhhhhhhhhhhhhhhh)  hhhhhhhhhhhhhhhhhhhhhhh   ********************   <-(bias-voltage)   |   
                                   hhhhhhhhhhhhhhhhhhhhhhh   (hhhhhhhhhhhhhhhhhhhhhh)                           |
     Left electrode           hhhhhhhhhhhhhhhhhhhhhhh   (hhhhhhhhhhhhhhhhhhhhhh)                           |
                                   hhhhhhhhhhhhhhhhhhhhhhh   (hhhhhhhhhhhhhhhhhhhhhh)                           | 
                                       
                                           Center region                     right electrode

14

General Questions and Answers / Transport calculation direction

« on: November 28, 2013, 18:13 »

As mentioned in the tutorials, the transport is only calculated in the Z direction. Does that mean the electrodes (left and right) should always have the same coordinates (in x and y directions) ?

I mean, for example, for the configuration below, is it possible to calculate its transport spectrum and I-V curves. etc with ATK?


----------------------> Z-direction
                                                                                                 X (or Y)-direction
(hhhhhhhhhhhhhhhhhhh)  hhhhhhhhhhhhhhhhhhhhhhh                                             /\
(hhhhhhhhhhhhhhhhhhh)  hhhhhhhhhhhhhhhhhhhhhhh                                              |
(hhhhhhhhhhhhhhhhhhh)  hhhhhhhhhhhhhhhhhhhhhhh                                              |   
                                   hhhhhhhhhhhhhhhhhhhhhhh   (hhhhhhhhhhhhhhhhhhhhhh)     |
     Left electrode           hhhhhhhhhhhhhhhhhhhhhhh   (hhhhhhhhhhhhhhhhhhhhhh)     |
                                   hhhhhhhhhhhhhhhhhhhhhhh   (hhhhhhhhhhhhhhhhhhhhhh)     |
                                       
                                           Center region                     right electrode

Really need to know this and thanks in advance.

Best