Messages

16

General Questions and Answers / Re: Inconsistency in the current analysis for InelasticTransmissionSpectrum

« on: January 9, 2019, 17:21 »

And as a result of  only integrating over only the bias window (-0.1ev, 0.1ev) , what is the true total current?  The one of ~10^-13 nA, or the one of ~ 10^-5 nA?
Does such difference mean there is strong phonon-assisted band-to-band tunneling occurred outside the bias window?

17

General Questions and Answers / Re: Inconsistency in the current analysis for InelasticTransmissionSpectrum

« on: January 9, 2019, 17:12 »

Thanks for the reply!
But the peak at -0.5 eV is also contributing to the total current, but why not take it into the integral? Instead, only the bias window (-0.1eV,0.1eV) is considered?
What I understand is that due to the phonon-assisted band-to-band tunneling effect, the tunneling at -0.5 eV is largely increased compared to the non-interacting case, and thus created a peak of 10^-5 nA in the spectral current.
In calculating the total current from the spectral current why don't we integral over all energy range to get a more accurate result?

Thanks!

18

General Questions and Answers / Re: Inconsistency in the current analysis for InelasticTransmissionSpectrum

« on: January 9, 2019, 04:40 »

Attached is the involved dynamic matrix and Hamiltonian Derivative scripts for calculating the InelasticTranmissionSpectrum.
I can not attach all my files in one time.

Thanks!

19

General Questions and Answers / Inconsistency in the current analysis for InelasticTransmissionSpectrum

« on: January 9, 2019, 04:38 »

Hello,
From the Inelastic Transmission Spectrum Analyzer I got the I-V curve (attached image.png) for 0-0.2V bias voltage and it can be noted that at bias = 0.2V the sum current (elastic current, inelastic current as well) is of ~10^-22 A = 10^-13 nA
However, I also generate its corresponding spectral current at 0.2V.(attached image-1.png), it can be approximated from the area under the curve that the current is ~10^-14  A= 10^-5 nA.
These two currents are supposed to be same with each other, but now they are 8 order of magnitude different.
Why is the case? Is this a bug in ATK?

Please check my attached scripts, I wonder if there is anything wrong in my calculation procedure.

Thank you! Any help is appreciated!

20

General Questions and Answers / Re: Current calculated from Inelastic transmission spectrum

« on: January 4, 2019, 17:19 »

Thank you for the reply!
How about the q points sampling?  Should I untoggle q_A and q_B periodicity too?

Thank you!

21

General Questions and Answers / Re: Current calculated from Inelastic transmission spectrum

« on: January 3, 2019, 17:52 »

Thank you for the reply!
So since by terminology the elastic current equals to non-interacting current then the current calculated from InelasticTransmissionSpectrum.elasticCurrent()
should be same or close to the current calculated from TransmissionSpeactrum.current()
But in this tutorial https://docs.quantumwise.com/tutorials/inelastic_current_in_si_pn_junction/inelastic_current_in_si_pn_junction.html
The TransmissionSpeactrum.current() is  -7.06766e-11 nA
while the InelasticTransmissionSpectrum.elasticCurrent() is -3.71e-09 nA
They are different by almost 2 magnitudes. I understand that they have different k-points sampling but does the k-points sampling really matter that much?

And speaking of the k-points sampling, for the quasi 1-D GNR system, in setting up the Inelastic transmission spectrum,  should I untoggle the periodicity in K_A and K_B and fix the k-points sampling as 1 in these two directions? 
And what about the q-points sampling, should I do the same thing, untoggling k_A and k_B periodicity?

22

General Questions and Answers / Re: Current calculated from Inelastic transmission spectrum

« on: January 3, 2019, 04:44 »

I think I have got the answer from the manual.
It says "If the non-interacting transmission is finite at the Fermi level (e.g. in a molecular junction with metallic leads) it will often be sufficient to calculate the inelastic transmission spectrum only at the Fermi energy and use the LOE current formula," and "In situations where there are no electrode states at the Fermi energy, like in a low- or un-doped semi-conductor, the direct use of the LOE and XLOE expressions will result in zero inelastic currents, when evaluated at the Fermi energy. In that case, the inelastic transmission spectra must be calculated at a range of energies (like the normal TransmissionSpectrum). "
So for my case I believe it is sufficient to take only the Fermi level and calculate the inelastic current.
But what if the non-interacting transmission at the Fermi level is finite but is a local minimal? (like in the attached image) In this case, is it still sufficient to take only the Fermi level for the inelastic current calculation?

In addition, I have a bit of confusion for the terminologies. I thought that the elastic current refers to the current calculated considering the elastic e-ph interaction, while the inelastic current refers to the current calculated considering the inelastic e-ph interaction.  But I learned from the manual that somehow elastic current equals to the non-interacting current. Why is this the case? But as shown in https://docs.quantumwise.com/tutorials/inelastic_current_in_si_pn_junction/inelastic_current_in_si_pn_junction.html. the elastic current is much larger than the current calculated from the normal TransmissionSpectrum which should be the non-interacting current.

23

General Questions and Answers / Current calculated from Inelastic transmission spectrum

« on: January 2, 2019, 20:58 »

Dear Quantumwise experts,
I am calculating the inelastic transmission spectrum of a GNR p-n junction (see attached python file for the configuration) using the InelasticTransmissionSpectrum method in ATK.
First I calculated the Transmission spectrum and PLDOS without the e-ph interaction, which gives a current I = -8.3168 e-5 nA.  As shown  In the attached image that from the spectral current and Projected Local Density of States it can be noticed the major current contribution is from the tunneling near the Fermi level. So I am expecting the sum current (elastic+inelastic) from the InelasticTransmissionSpectrum is several magnitudes larger than that from the TransmissionSpectrum as is shown in the  case study of https://docs.quantumwise.com/tutorials/inelastic_current_in_si_pn_junction/inelastic_current_in_si_pn_junction.html
I just wonder that is it possible to get a reasonable current by just taking one or a few representative energy points in the InelasticTransmissionSpectrum method parameter setup, e.g.  0 eV or (-0.05, 0, 0.05)*eV ?
Since the spectral current at these energies is largest.
I have the InelasticTransmissionSpectrum sum current for  0 eV which is -1.38e-4 nA (one magnitude larger than the non-interacting case) and for (-0.05, 0, 0.05)*eV which is -5.84e-5 nA. (slightly smaller than the non-interacting case)
They are quite different, but which one is more accurate?  Or maybe neither?

Thank you!
Happy New Year!

24

General Questions and Answers / Re: The not responding issue of 2017 version VNL

« on: November 30, 2018, 03:06 »

Thank you for the reply.
I believe it is the case. I think I just have too many files in my project.
Why the VNL run through all of them at the startup even though  I am not trying to open any file but simply open the VNL itself?

25

General Questions and Answers / The not responding issue of 2017 version VNL

« on: November 28, 2018, 19:10 »

Hi,
Every time I try to open the VNL on my laptop it stuck and show the "not responding"  for a while, sometimes 10 mins, 20mins, and then it resumes normal to use.
This issue bothers a lot. Is there a way to solve this?

26

General Questions and Answers / Re: The current minimum points shift with temperature

« on: November 5, 2018, 04:21 »

Thank you for your reply!
In a FET device, if we change the gate voltage V_g, the energy position of the conduction band and valence band will change. If we define a ratio r as the change in V_g and its caused CB and VB energy position change ΔE i.e. r = ΔV_g/ΔE.
I just find from the analysis of PLDOS that such ratio r changes with temperature for calculations of STD configuration, while in calculations for pristine configuration, such ratio r remain invariant of temperature.
I think that could be a reason for the current minimum point change with temperature in the STD I_V curves. But still, I am interested in such changes of r with temperature, because this would lead to big device performance change.
I have read through the paper about the STD method PhysRevB.96.161404 many time and I cannot find anything that possibly related to this topic.
Is there any more physical explanation about this changes?

Thanks for your help!

27

General Questions and Answers / The current minimum points shift with temperature

« on: November 3, 2018, 03:36 »

Hi,
I have calculated the transfer characteristics for a GNR TFET device considering the electron-phonon interaction using the STD method at different temperatures, as shown in the left image of the attached file.
I also calculated the transfer characteristics for its corresponding pristine configuration ( no e-ph interaction) at different temperatures, as shown in the right image of the attached file.
In the pristine I_V curves, the current minimum point at all temperatures are all aligned at about 1.2 V.
However, in the STD I_V curves, there are not aligned: the I_min point shift to the left as temperature increases.
I was using the Slater-Koster method with the DFTB Hotbit basis to calculate for both the STD and pristine configurations.
I just wonder why the I_min points in the STD I_V curves do not align. Is this a physical phenomenon or is this something to do with the STD method?

Thanks!

28

General Questions and Answers / How to Choose properly the E0 and E1 for using Energy interval method

« on: November 1, 2018, 19:41 »

Dear Quantumwise Experts,
In calculating the Inelastic transmission spectrum, there is a speed-up method called "Phonon Energy Intervals" that instead of calculating explicitly all the 3N phonon modes of the device, it groups the 3N modes into M energy intervals and we will only need to calculate these M new effective phonon modes. So that it is much faster.
My question is to choose E₀ and E₁, how to ensure the energy interval [E₀,E₁] span that of the phonon modes of the calculated dynamical matrix.  Is there a way to check the relevant information from the dynamical matrix object?

29

General Questions and Answers / Re: Trying to understand the Inelastic Transmission Spectrum Analyzer

« on: October 26, 2018, 19:12 »

Thank you for replying!
So can we think these phonon modes in the supercell at Gamma point as the linear combinations of the two phonons modes in the primitive cell at gamma point, with 0meV and 65meV energy, respectively? i.e. q = aq₁ + bq₂., and q₁ and q₂ are the two phonon modes in the primitive cell at gamma point.
So that they have so many possible energy?
Is my understanding here correct?

30

General Questions and Answers / Re: Specify (identify) the effect of phonons on carrier transportation

« on: October 23, 2018, 16:20 »

Can anyone answer my question? Please help!