QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: J.g_johnson on November 25, 2014, 14:22

Title: Calculating the conductance for different gate potentials
Post by: J.g_johnson on November 25, 2014, 14:22

Hi,
   In the tutorial of "Graphene Junction Device", it shows how to calculate the conductance for different gate potentials and temperature at the same time.
http://quantumwise.com/documents/tutorials/latest/GrapheneDevice/index.html/chap.gatepotential.html
   
But here I want to calculate the  conductance for different gate potentials at 300K lonely. So how to modify this script:

#make list of relevant temperatures
temperature_list=numpy.linspace(0,2000,21)*Kelvin
#make list of relevant gate voltages
gate_voltage_list=numpy.linspace(-2.0,2.0,17)*Volt
#make list to hold the conductance calculations
conductance_list=numpy.zeros(len(gate_voltage_list)*len(temperature_list))
conductance_list=conductance_list.reshape(len(gate_voltage_list),
                                          len(temperature_list))

#specify the filename for the netcdf data file
filename="gatescan-6-6.nc"
#loop through the gate voltages
for n in range(len(gate_voltage_list)):   
    transmission_spectrum=nlread(filename,
                                 object_id="trans"+str(gate_voltage_list[n]))[0]
    #loop through the temperature list
    for i in range(len(temperature_list)):
        conductance_list[n,i]=transmission_spectrum.conductance(
            electrode_temperatures=(temperature_list,temperature_list))

#plot the conductance as function of gatevoltage
import pylab
pylab.figure()
# make curve for each temperature
for i in range(len(temperature_list)):
    pylab.semilogy(gate_voltage_list,conductance_list[:,i])
pylab.xlabel("Gate Voltage (V)")
pylab.ylabel("Conductance (S)")
pylab.show()

Thanks!

Title: Re: Calculating the conductance for different gate potentials
Post by: zh on November 26, 2014, 01:24

"temperature_list=numpy.linspace(300,300,1)*Kelvin"
will give one temperature (300 K) in the "temperature_list".

Title: Re: Calculating the conductance for different gate potentials
Post by: J.g_johnson on November 26, 2014, 02:40

Yes, It works!  Thank you very much!

Title: Re: Calculating the conductance for different gate potentials
Post by: J.g_johnson on November 26, 2014, 03:17

Another question is that the unit of calculated conductance is "S". So how to translate it into "G0" as unit of conductance. According to my experience, "S"*12906.4="G0". But I am not sure whether it is right.  So is there any relationship or formula between unit of "S" and "G0".

Title: Re: Calculating the conductance for different gate potentials
Post by: zh on November 26, 2014, 08:02

http://en.wikipedia.org/wiki/Conductance_quantum
http://physics.nist.gov/cgi-bin/cuu/Value?conqu2e2sh
conductance quantum, denoted by the symbol G0 is the quantized unit of electrical conductance. It is defined as:
G0 = 2 e^2/ h = 7.7480917346(25)×10^{−5} S
where h is Planck's constant.

Title: Re: Calculating the conductance for different gate potentials
Post by: J.g_johnson on November 26, 2014, 08:09

yes, Thank you!

Title: Re: Calculating the conductance for different gate potentials
Post by: abhi005 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.

Title: Re: Calculating the conductance for different gate potentials
Post by: Anders Blom on January 14, 2015, 12:55

Considering the dramatic increase in current with temperature, you probably are looking at a system with a large band gap, and the current you get for 1200 K is do to thermionic emission. Perhaps you need to consider other mechanisms, like doing, to get a larger electron concentration in the conduction band.

Title: Re: Calculating the conductance for different gate potentials
Post by: abhi005 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.

Title: Re: Calculating the conductance for different gate potentials
Post by: Umberto Martinez on January 16, 2015, 09:17

that depends, of course they should not be different if you follow the tutorial.
but what do you mean with different results? which results? can you post them?
can you include your device geometries?
which ATK version are you using?

Title: Re: Calculating the conductance for different gate potentials
Post by: abhi005 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

Title: Re: Calculating the conductance for different gate potentials
Post by: Umberto Martinez on January 17, 2015, 19:20

something like this:

Code

device_configuration = nlread("z-a-z-6-6.nc",DeviceConfiguration)[0]

calculator = device_configuration.calculator()
metallic_region0 = device_configuration.metallicRegions()[0]

gate_voltage = ...
sd_voltage = ...

device_configuration.setMetallicRegions(
    [metallic_region0(value = gate_voltage)] )
device_configuration.setCalculator(
      calculator(electrode_voltages=(-0.5*sd_voltage,0.5*sd_voltage)), 
      initial_state=device_configuration)

...