QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: Shan on July 10, 2015, 14:05

Title: Gate ineffective in tunnel junction device, ?
Post by: Shan on July 10, 2015, 14:05

Dear QW team,

I have test created a tunnel junction device and tried to plot its IV (current-voltage) characteristics at different gate voltages. I used anthracene molecule as a tunnel island. Used extended Huckel model to plot the IV curves.

Though I varied the gate voltage, no changes were observed in the IV plot. I observed same IV plot at gate voltage of 0V and 2V.

can u please explain me.... what is wrong here... and why the gate become ineffective in supplying energy to the island. (dielectric constant of dielectric layer is taken as 10 epsilonzero).

 Here I am attaching the configuration, and curves.

Title: Re: Gate ineffective in tunnel junction device, ?
Post by: Umberto Martinez on July 13, 2015, 08:32

The relevant states of the molecules are probably not modified so much by the applied gate.
It can be interesting to plot device density of states projected into the molecules atoms and orbitals to see how these are effected by the gate bias.
Also, if you provide your input script we can say if there is something very wrong in the initial set up.

Title: Re: Gate ineffective in tunnel junction device, ?
Post by: Shan on July 14, 2015, 14:52

Here I attached the script as you requested..

Please have a look sir....

Title: Re: Gate ineffective in tunnel junction device, ?
Post by: Umberto Martinez on July 14, 2015, 16:07

Ok, I definitely missed your picture before.
Please increase your central region size and electrodes as well.
there are no gold atoms in the central region, excluding the electrode extension region.

Please have a look here for the construction of a device configuration: http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/chap.negf.html

Title: Re: Gate ineffective in tunnel junction device, ?
Post by: Shan on July 27, 2015, 14:10

Sir,

I increased the central region size and performed the IV calculation using exteneded Huckel (Device) calculator... but result is same at 0 and 2 V gate voltage.
 I also tried DFT (device) but got an error message.

can u please clarify the reason sir.

below is the structure py file.

Title: Re: Gate ineffective in tunnel junction device, ?
Post by: Shan on November 19, 2015, 15:13

QW team.... reply please...

Title: Re: Gate ineffective in tunnel junction device, ?
Post by: Anders Blom on November 19, 2015, 23:43

You are running a non-selfconsistent calculation, so the gates never enter the equations. They are only taken into account during selfconsistency.