Effect of gate metal

[tara]

In the post
http://quantumwise.com/forum/index.php?topic=2964.msg13890#msg13890,  i understood how the  Id-VG curve shifts based upon the gate  metal in the case when both electrodes are  of same material.

But How to calculate the shift in the Id -Vg curve if both electrodes are of  different materials??

[kstokbro]

When your two electrodes are of different materials, they may have a different work functions, i..e their fermi levels are different. When you form the two probe, at zero bias the two fermi levels are alligned and it is now the two vacuum levels that are different. In the output file we report the value of the fermi levels, lets call that value Ef

Now you put in a  metallic region as gate. If you specify the gate potential to zero, it will correspond to modelling a gate material with work function W=-Ef with a applied gate potential zero. However, if you would like to model another gate material with work function W1, you actually need to apply a potential V  to simulate the situation of a zero gate potential V1=0.

Thus, the relation between the experimental gate potential V1, and the calculational gate potential V, is
V = V1+W1+Ef

Thus, if you have a calculation with Isd versus Vgate, you can transform it to a physical gate using the transformation
V1 = Vgate - (W1+Ef)

[tara]

thanks a lot:) indeed helpful

[Hassan]

Can you please describe in detail where/how the Fermi level is reported?

[Umberto Martinez]

Add the Chemical Potential analysis
See Reference Manual here http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.chemicalpotential.html
Left and right chemical potentials are also written in the log file

[tara]

The relation between the experimental gate potential V1, and the calculational gate potential V, is
V = V1+W1+Ef  as mentioned earlier in the post

However the units of W1 and Ef are in "electron volts(ev)" whereas the gate voltages V1 and V are in "volts".
Could you explain me this??

[Anders Blom]

As long as you are dealing with electrons, the units are basically interchangeable, with the possible change of sign. Just consider the definition of the eV unit!