The current minimum points shift with temperature

[weixiang]

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!

[Petr Khomyakov]

Is this a physical phenomenon or is this something to do with the STD method?

What do you mean? Special thermal displacement accounts for elastic electron-phonon interaction, which is a physical phenomenon. I guess the I-Vg profile depends on the system of study, and you should do the analysis of your results, trying to understand what governs the behavior of the device. There are many analysis tools that allows you doing it, e.g., band structure of the pristine material, PLDOS, Transmission spectrum. 

[weixiang]

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!

[Petr Khomyakov]

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?

I think that PRB paper is not the only one on the effect of elastic electron-phonon scattering on the charge carrier transport in devices. There must be a plenty of literature about it.  I would suggest you searching for that and reading that to get a better idea on your results.