transport in pure materials

[nazi]

Dear experts,

In the Datta's book say that:
"We can easily see that the resistance G^-1 is associated with the interfaces and not with the conductor itself"

But my results show that calculating the current under bias voltage in a pure 2D system depends on the length of the scattering region. Also, this dependent is not linear, for example, under bias voltage 2V the calculated current in the larger system is 1/3 of the current of the smaller system but under bias voltage 3 this ratio could be different. The current intensity is in the order of several micro Amper.

As the system is pure and there is no scatterer in the system, what is the reason of this behavior?

Second question: is the implemented method in quantumwise valid for such a study (calculating current under bias-voltage in a 2D system)?

I really appreciate your help in advance.
Nazi

[Petr Khomyakov]

QuantumATK is valid for calculating the current vs bias voltage for 2D systems. Please read carefully at least the first two chapters of Datta's book to understand the issue. Your calculations do not contradict what is said in the book, but rather confirm it. As I said your IV calculations dot not make sense for perfect system, as also suggested by Datta's book. This is because the scatters (defects, interfaces, phonons) in the conductor (central region) make the potential drop to take place across the conductor only, and the potential profile should be flat in the leads for any choice of the central region (=conductor+electrode extensions) length.

[nazi]

Dear Petr,

Thank you for your response.

So what shall we do to study the transport properties of a pristine system under bias voltage?
Maybe just by considering the zero-bias transmission; but in this regards, we cannot find for example NDR characteristic in the IV curve of a system.

Thanks in advance for your answer.

Nazi

[Petr Khomyakov]

I would guess that you should consider a more realistic device structure, e.g., with doped electrodes or more realistic metal electrodes.  This is totally up to you on how to design the model device, and the QuatumATK will give you the result within the approximations of the model adopted, but making a physically-appealing, relevant model is up to a human, not a software package.

[nazi]

Dear Petr,

As I explain in my last post, as there is no scatterer in the central region of my device, I can't understand the dependence of current intensity to the length of the central region.

Regards to your answer, this problem arises by the non-metallic electrodes?

If I have metallic electrodes, the current intensity passes true the pure scattering region does not change by changing the length of scattering region?

I really appreciate your help.

Regards,
Nazi

[Petr Khomyakov]

If I have metallic electrodes, the current intensity passes true the pure scattering region does not change by changing the length of scattering region?

To answer all the questions, you have to do a research study on the topic.   

[nazi]

Dear Petr,

I have used the metallic electrodes in my device; however, the central scattering region is pure 2D phosphorene without any defects.
But the calculated current shows that it is again length dependent. by increasing the length of scattering region the current intensity decreases.
As there is no scatterer in the central region, I don't understand this behavior.
Would you please explain it to me?

I really appreciate your help in advance.

Regards,
Nazi

[Petr Khomyakov]

Now, it really depends whether you want to study ballistic conductor or conductor with scatters, e.g., conductor with thermal disorder (electron-phonon elastic scattering), see  https://docs.quantumwise.com/casestudies/std_transport/std_transport.html, or introduce some defect(s), or impurities, or artificially dope the material as described in https://docs.quantumwise.com/tutorials/inas_p-i-n_junction/inas_p-i-n_junction.html.

I strongly encourage you to do some reading on the quantum transport topic for interpreting your numerical results.  This is a good practice for a serious researcher. Please do your homework.

[nazi]

Thank you Petr for your useful guides.
I am doing my homework but the results are sometimes strange for me and I need help to understand.   

Again thank you very much for your help.

Regards,
Nazi

[nazi]

Dear Petr,

I know the e-ph interactions could be important in the transport results; however, I ignore this interaction.
 I would like to study transport in a pure system without any dopant in the central region;  the leads are metal but the central region is pure without any defects.

The simulation of such a system is not physically true? why?

From your response, I think we are forced to consider some scattering centers in the system.

Thank you.
Nazi

[Petr Khomyakov]

I did not say that you cannot study the electron transport through a ballistic conductor. It is totally up to you and your research project goals.