In this tutorial, we will write a python script to compute the transfer characteristic of a double gate CNT-FET transistors, with doped reservoirs (molar fraction = 5e-3), 1.5 nm oxide thickness, 5 nm channel length. The applied Vds=0.1V and the Vgs is swept in the interval 0<=Vgs<=0.5 V.
Tutorial 06: transfer characteristics
Let’s import the module as usual
from NanoTCAD_ViDES import *
and define the nanotube. The channel is 5 nm, the doped source
and drain reservoirs are 5 nm each, so the total length of the nanotube
is 15 nm.
I take care of the grid, using the same grid along the x and y axis,
while for the z-axis, I use the same discretization as the C atoms
along the z-axis
I take care of the gates, which are aligned with the channel (i.e.
no underlap, no overlap).
I then define the dielectric which embeds the CNT, which
is SiO2: so I have to define the correct relative dielectric constant
of the SiO2
I then create the interface to pass all the parameters within the
self-consistent Poisson/NEGF iterative scheme,
and I then dope the source and drain reservoirs, with a molar fraction equal to 5e-3
I want to work within the mode space approach, using two modes, so I do the following:
I now take care of the applied gate voltage: Vds=0.1, so CNT.mu1=0 (by default)
The sweep start from Vgmin=0V and ends at Vgmax=0.5V.
The step is equal to Vgstep=0.05V
I need to store the computed current for each Vgs in somewhere
Then I go on with the while cycle.
At each step I have to modify the Fermi level of each gate, and then I have
to make these changes effective, by applying the command set_gate.
In addition, in the case of the first computed voltage, I first compute the initial
solution through the solve_init command. In the following step, I start from
the solution computed at the previous step.
# I set the Fermi level of the top and bottom gate
#If the first voltage, then I compute the initial solution
# I compute the initial solution
print “Computing the initial solution”
I then save the computed transfer characteristic in a file