Every software package contains a full set of examples suitable for that version and are installed with the software. If you see examples here that are not in your installation you should consider updating to a later version of the software. These examples can be used by beginners and advanced users for product evaluation, teaching purposes, and self-training.

Required Modules

Victory Atomistic

How to compute the transfer characteristic I(V) of a Si NWFET, within the self-consistent Born approximation and using modespace.

This example demonstrates the use of a device template combined with a metasolver to simulate a nanowire FET in NEGF.

vaex03.in is a Victory Atomistic compact input deck including:

-A silicon nanowire-FET (NWFET) described in tight-binding

-A recursive Green’s Function algorithm coupled with a Poisson solver

– A self-consistent Born treatment of electron-phonon (e-ph) scattering.

– A generalized low-rank approximation using a unitary matrix projection.

The user sets the number of self-consistent Born iterations: from 0 = ballistic mode to a moderate number (15-20) insuring the self-consistency of the e-ph interactions and current conservation.

1. Device Template NanowireStandard_tb
A silicon nanowire of type N-I-N with a cross-section of 4-by-4 unit cells with a length of 65 unit cells (2.17 nm x 2.17 nm by 35.30 nm), is set up with a sp3d5s* tight-binding basis.
The device is composed of five sections of equal lengths:
. source (2),
. spacer-source (5),
. channel (1),
. spacer-drain (6),
. drain (3),
. gate-oxide (4), with a gate-all-around geometry around the channel.

2. Metasolver MetaSCBorn
As a test case, a voltage ramp Vg from 0.8V to -0.1V is applied to the gate with a fixed Vds = 0.3V.
Checkpoint/restart options allow to interrupt and resume the simulation from the last voltage point, or from any other voltage point, thanks to the Backup_History* files.
The user defines the temperature and the acoustic and optical phonon parameters.
We use silicon bulk parameters for this example at room temperature.
Other electron-phonon mechanisms are also possible:
. polar-optical
. roughness scattering
. impurity scattering
. remote Coulomb scattering
We keep the most essential scattering states thanks to a modespace optimization compatible with the self-consistent Born approximation.
A specific file contains the low rank approximation (LRA) matrix used for modespace, defined by the unitary_matrix_filename option.

3. Visualization with Victory Visual
a. vtk structures
. device_structure.vtk: device structure with regions [1-5] with different colors,
. scborn__poisson_deviceXXXmV.vtk: atomic-scale resolved electrostatic potential and charge in 3D,
. scborn__poisson_deviceXXXmV_filtered.vtk: same data excluding a specific region(s) like the gate oxide and spacers.
b. Potential profile and IV
. scborn__poisson_device_1D_X.XXV.dat: 1D potential and bands profiles along a given direction,
. scborn__ramper_IV.dat: I(V) transfer characteristic.
c. Density of States
. scborn__lra_module_retarded_energy_resolved_density_of_states_X.XXV_output_along_a_line.dat:
the density of states resolved in energy and space along a given direction.

Note: a full I(V) curve takes approximately 4 hours with one node and 24 CPU cores in ballistic mode (=0 iteration of SC-Born).
Note: To visualize 1D band profile at Vg = 0.7 V, the file has to be opened in victory visual, then select “Reinterpret as a plot ” from top bar. Tick “Ec_confined_no_strain ” and untick the rest.
Note: To visualize DOS(E,x) at Vg = 0.7 V, the file has to be opened in victory visual, then select “Convert to LDOS for Local Density of States visualization “

Images