Messages

1

General Questions and Answers / Re: How to get Contact Resistance in ATK

« on: May 15, 2015, 15:29 »

hi ZH,
i have simulated cnt fet . i got results like Id vs Vgs and Id vs Vds now i want to calculate trans conductane of this fet. HOW can i do that? please reply asap.

2

General Questions and Answers / Re: optimum K-points for convergence

« on: February 28, 2015, 11:37 »

thanks for your reply sir,
yes sir it is not converging for negative voltages.
i first calculate transmission spectrum for 0 bias then i make a loop to calculate the transmission spectrum for other bias and with the help of these transmission spectrum i can calculate curves for current.Is this the correct way to calculate current?
i also increase the electrode size and electron temperature to 2000, because electron temperature has its effect on convergence.
am I doing correct changes?

3

General Questions and Answers / Re: optimum K-points for convergence

« on: February 26, 2015, 11:36 »

sir , i am trying to simulate a cntfet with drain voltage 1.5v and gate voltage from -2 to +2 .geometry is converged for gate voltage .2 to 1v but did not converge for other voltages .
what should be the k-point sampling? i took 1,1,300, is it correct?
cntfet is 16 A long with gate of 12 A.

4

General Questions and Answers / Re: Calculating the conductance for different gate potentials

« on: January 16, 2015, 13:53 »

hi umberto,
thanks for your reply
yes i was making some mistake now i have removed that one.
i want to change both gate voltage and drain voltage simultaneously but in the graphene junction tutorial i can change only one voltage either gate voltage or drain voltage and i have to fix the other voltage .
please tell me what changes i have to make in the scripts given in the graphene junction tutorial to vary both gate and drain voltage simutaneously.

http://www.quantumwise.com/documents/tutorials/latest/GrapheneDevice/index.html/chap.current.html

5

General Questions and Answers / Re: Calculating the conductance for different gate potentials

« on: January 16, 2015, 06:26 »

hi andors blom
thanks for your reply
I tried Id-Vds calculation using calculator iv(analysis) option and by using the script given in the tutorial
http://www.quantumwise.com/documents/tutorials/latest/GrapheneDevice/index.html/chap.current.html
surprisingly i obtain different result for the same geometry . is it possible?
please guide me in this matter.

6

General Questions and Answers / Re: CNTFET using doped electrodes

« on: January 14, 2015, 10:16 »

hi
i am making cntfet. my channel ic 10nm long what should be the length of electrode. i also doped the electrode with charge =-.01 .i simulate my geometry with the default electrode length which came during bulk to device conversion in my case it is 10 Ang.
is this electrode length length is correct or i have to make some change?

7

General Questions and Answers / Re: Calculating the conductance for different gate potentials

« on: January 14, 2015, 09:53 »

hi i am making an cntfet.i have some doubts like
what should be the exact(one) value of temperature in the temperature list? is it 300k?
as i increase this temperature my iv characteristics are improved and quite good at 1200k but not good at 300k.
i am attaching two pics in both the pics i varied gate voltage from -2 to 2 and electrode voltage is fixed at .2v
i have also used the same script as discussed in the earlier posts.

8

General Questions and Answers / Re: CNTFET using doped electrodes

« on: December 26, 2014, 06:26 »

hi anders blom,
sorry for not giving information .I am attaching snapshot of the error coming during the simulation. It  shows memory error but there are some others error too.please suggest me about the remaining errors. i am also attaching script of my geometry.

# Set up configuration
central_region = BulkConfiguration(
    bravais_lattice=central_region_lattice,
    elements=central_region_elements,
    cartesian_coordinates=central_region_coordinates
    )

# Add metallic region
metallic_region_0 = TubeRegion(
    0.0*Volt,
    start_point = [23.9255, 23.9255, 10.0]*Angstrom,
    end_point = [23.9255, 23.9255, 91.46]*Angstrom,
    inner_radius = 15.0*Angstrom,
    thickness = 1.0*Angstrom,
)

metallic_regions = [metallic_region_0]
central_region.setMetallicRegions(metallic_regions)

# Add dielectric region
dielectric_region_0 = TubeRegion(
    25.0,
    start_point = [23.9255, 23.9255, 10.0]*Angstrom,
    end_point = [23.9255, 23.9255, 91.46]*Angstrom,
    inner_radius = 5.0*Angstrom,
    thickness = 10.0*Angstrom,
)

dielectric_regions = [dielectric_region_0]
central_region.setDielectricRegions(dielectric_regions)

device_configuration = DeviceConfiguration(
    central_region,
    [left_electrode, right_electrode]
    )

# -------------------------------------------------------------
# Calculator
# -------------------------------------------------------------
#----------------------------------------
# Basis Set
#----------------------------------------
basis_set = [
    CerdaHuckelParameters.Carbon_graphite_Basis,
    CerdaHuckelParameters.Carbon_graphite_Basis,
    ]

#----------------------------------------
# Numerical Accuracy Settings
#----------------------------------------
left_electrode_numerical_accuracy_parameters = NumericalAccuracyParameters(
    electron_temperature=1200.0*Kelvin,
    k_point_sampling=(1, 1, 300),
    density_mesh_cutoff=150.0*Hartree,
    )

right_electrode_numerical_accuracy_parameters = NumericalAccuracyParameters(
    electron_temperature=1200.0*Kelvin,
    k_point_sampling=(1, 1, 300),
    density_mesh_cutoff=150.0*Hartree,
    )

device_numerical_accuracy_parameters = NumericalAccuracyParameters(
    electron_temperature=1200.0*Kelvin,
    k_point_sampling=(1, 1, 300),
    density_mesh_cutoff=150.0*Hartree,
    )

#----------------------------------------
# Iteration Control Settings
#----------------------------------------
left_electrode_iteration_control_parameters = IterationControlParameters()

right_electrode_iteration_control_parameters = IterationControlParameters()

device_iteration_control_parameters = IterationControlParameters()

#----------------------------------------
# Poisson Solver Settings
#----------------------------------------
left_electrode_poisson_solver = MultigridSolver(
    boundary_conditions=[[NeumannBoundaryCondition,NeumannBoundaryCondition],
                         [NeumannBoundaryCondition,NeumannBoundaryCondition],
                         [PeriodicBoundaryCondition,PeriodicBoundaryCondition]]
    )

right_electrode_poisson_solver = MultigridSolver(
    boundary_conditions=[[NeumannBoundaryCondition,NeumannBoundaryCondition],
                         [NeumannBoundaryCondition,NeumannBoundaryCondition],
                         [PeriodicBoundaryCondition,PeriodicBoundaryCondition]]
    )

device_poisson_solver = MultigridSolver(
    boundary_conditions=[[NeumannBoundaryCondition,NeumannBoundaryCondition],
                         [NeumannBoundaryCondition,NeumannBoundaryCondition],
                         [DirichletBoundaryCondition,DirichletBoundaryCondition]]
    )

#----------------------------------------
# Device Algorithm Settings
#----------------------------------------
device_algorithm_parameters = DeviceAlgorithmParameters(
    initial_density_type=EquivalentBulk(electrode_constraint_length=10.0*Angstrom),
    )

#----------------------------------------
# Electrode Calculators
#----------------------------------------
left_electrode_calculator = HuckelCalculator(
    basis_set=basis_set,
    charge=-.01,
    numerical_accuracy_parameters=left_electrode_numerical_accuracy_parameters,
    iteration_control_parameters=left_electrode_iteration_control_parameters,
    poisson_solver=left_electrode_poisson_solver,
    )

right_electrode_calculator = HuckelCalculator(
    basis_set=basis_set,
    charge=-.01,
    numerical_accuracy_parameters=right_electrode_numerical_accuracy_parameters,
    iteration_control_parameters=right_electrode_iteration_control_parameters,
    poisson_solver=right_electrode_poisson_solver,
    )

#----------------------------------------
# Device Calculator
#----------------------------------------
calculator = DeviceHuckelCalculator(
    basis_set=basis_set,
    numerical_accuracy_parameters=device_numerical_accuracy_parameters,
    iteration_control_parameters=device_iteration_control_parameters,
    poisson_solver=device_poisson_solver,
    device_algorithm_parameters=device_algorithm_parameters,
    spin_polarization=Unpolarized,
    electrode_calculators=
        [left_electrode_calculator, right_electrode_calculator],
    )

device_configuration.setCalculator(calculator)
nlprint(device_configuration)
device_configuration.update()
nlsave('ex7gate10.nc', device_configuration)

# -------------------------------------------------------------
# Transmission spectrum
# -------------------------------------------------------------
transmission_spectrum = TransmissionSpectrum(
    configuration=device_configuration,
    energies=numpy.linspace(-2,2,101)*eV,
    kpoints=MonkhorstPackGrid(1,1),
    energy_zero_parameter=AverageFermiLevel,
    infinitesimal=1e-06*eV,
    self_energy_calculator=RecursionSelfEnergy(),
    )
nlsave('ex7gate10.nc', transmission_spectrum)
nlprint(transmission_spectrum)

9

General Questions and Answers / Re: CNTFET using doped electrodes

« on: December 24, 2014, 09:27 »

i am also trying to replicate your above result but could not succeeded. It is not showing any error but could not run and failed after starting huckel device calculation.please suggest me.
i am also attaching how execution stops without showing any error.

10

General Questions and Answers / Re: CNTFET using doped electrodes

« on: December 24, 2014, 07:16 »

hi i am also working on cntfet.i am also using dielectric and my channel is 10 nm long.i have some queries...
1. why negative gate voltage on the gate ?
2. when i used channel completely covered with gate than it shows error. is it necessary to use gate like you have used in the upper geometry?
if you can provide me some more information about your geometry and calculator settings than it could be very useful for me.
tahnks in advance.

11

General Questions and Answers / Re: boundary condition

« on: December 23, 2014, 14:29 »

thanks for your reply.i am not getting how it can be done. Can you please tell me how can I converged my geometry with one boundary condition and then how can I use this converge state for further calculations.

12

General Questions and Answers / boundary condition

« on: November 17, 2014, 15:55 »

i am making an cntfet.i dont know which boundary condition are best for my device.i have choosen neuman but the multigrid residual error is infinite. so i choose drichlet for B bottom and neumann for all others then error is less but quite large(e+000).so i choose drichlet for B bottom A front A back and neumann for B top.now error is quite small(e-010).so my question is

1.Does drichlet condition can be consider for device with gate?

13

General Questions and Answers / Re: Computed residual : 1.#INF0e+000 #

« on: November 13, 2014, 14:28 »

thanks for your reply.I have done what you have suggested but still it shows infinity error.I think it is the problem of poission solver settings.I have choose neumann for both A and B.So i tried by changing these condition by setting B Bottom drichlet and now error is not infinity but quite large in the range of e+000.please suggest me in this direction .Am i going in right direction?

14

General Questions and Answers / Re: what kind of Muti-grid should be choosen when calcult graphene_bulk transmission

« on: November 13, 2014, 14:18 »

please suggest me what type of multigrid i have to choose for CNT fet.I have choosen neumann but it shows infnity error then i choose drichlet for B Bottom again error is quite large in the range of e+000.i am also attaching .py file.please help me out of this problem.

15

General Questions and Answers / Re: Warning Message

« on: November 12, 2014, 14:00 »

thanks anders blom for your reply....actually i didnt know that INF means infinity.