Topics

1

General Questions and Answers / General Questions

« on: October 4, 2012, 06:24 »

Dear QuantumWise team,

I've been exploring ATK and have come up with a few general questions:

1. As I understand, the electron concentration can only be calculated with the DFT package.  If I'm using the semi-emprical Huckel model I cannot determine the concentration.  What is the reason for that? 

2. I've looked in the manual, and tutorials, but I still have trouble understanding the meaning of ElectronDifferenceDensity. Could someone please elaborate on that or refer me to a detailed explanation? Could I extract electron concentration from this?

3. In the "ballistic coherent tunnelling current" regime, an electron accelerates indefinitely in the central region (due to a finite voltage bias between the two terminals) until it reaches an electrode where it is absorbed or is scattered in the central region if there are deformities from periodicity, there is no drift or diffusion currents...true or false? In this way, does it matter what material type one is using if its perfectly periodic?

4. When the transmission coefficient is calculated, the user has the option to define the energy range.  Later, the product of the transmission coefficient and the fermi function is integrated over that range to give an electric current.  If one computes for larger energy range, you would get a larger current and if one computes for narrower range, smaller current.  How can I determine the correct range that will give accurate current?

5. How can I plot the electric field strength in the XY plane in the scattering region?

6. Can the physical temperature of a device configuration be adjusted? How?

Kind Regards,
gM

2

General Questions and Answers / Bias loop question

« on: September 18, 2012, 16:18 »

Dear All, I have a small question about creating a bias loop.  What difference does it make (if any) between creating a bias loop like this:

for bias in numpy.arange(0.,1.,0.1)*Volt:
    device_configuration.setCalculator(
        calculator(electrode_voltages=(0.5*bias,-0.5*bias)),
        initial_state=device_configuration
        )

versus one like this:

for bias in numpy.arange(0.,1.,0.1)*Volt:
    device_configuration.setCalculator(
        calculator(electrode_voltages=(bias,0)),
        initial_state=device_configuration
        )

Aka. varying both terminals versus varying one terminal and keeping the other grounded with an equivalent potential difference in both cases.
Regards.

3

General Questions and Answers / Ballistic transport

« on: August 24, 2012, 00:55 »

Hello and thank you for reading.  With respect to ballistic transport, if the length of a metallic wire is increased passed the mean free path of the metal, then ballistic regime is no longer dominant as there is scattering.  I was wondering if ATK can capture this phenomenon and if there have been experiments/scripts on this?

Regards.

4

General Questions and Answers / Gold simulation

« on: July 10, 2012, 18:46 »

Hi all and thank you for your attention  .  I simulated the IV characteristics from (-0.3V to 0.3V) of three gold wires with dimensions:

Contact Length (z direction)          Width of wire (y direction)            Central region length (z direction)
8.16A                                                    20A                                             26.4A
8.16A                                                    20A                                             30.6A
8.16A                                                    20A                                             51.2A

For all three I used k-point sampling of 1,1,100 for left/right electrode accuracy.

The IV characteristics of all three structures look nearly identical when they should theoretically change slope as the resistance of a longer piece of metal should increase and hence less current should pass through. Would you be able to tell me what I may be doing wrong here?  I have attached the three scripts for the devices as well as the result I got.

5

General Questions and Answers / Nanoscale MOSFET with ATK

« on: June 8, 2012, 23:30 »

Hello, and thank you again for taking the time to look at my inquiry. I'd like to understand better, what are the capabilities of ATK to simulate a nanoscale device such as the one attached (very primitive version of a 5nm mosfet).

1.How do I define meaningful electrode regions? Must they be metal? Should the lattice extension of the semiconductor channel extend in the contact region (see attached)? 
2.How exactly are these electrode regions contacted?  Is the cross-section of the contact vertical or horizontal?
3.What is the simulation time of a device in the ~1000 atom range on 4 Quad core machines with 8 GB of ram using MPICH2? Does the simulation time increase linearly with number of atoms, is it NlogN, N^2..etc?
4.Is there a tutorial, script, resource, etc. that goes in detail about how to simulate nanoscale MOSFETs using ATK?

Kind Regards.

6

Scripts, Tutorials and Applications / How to define ohmic contacts

« on: May 29, 2012, 22:00 »

Hello,  I've been struggling with this for a while.  I'd like to know how to define ohmic contacts in ATK so that I could simulate IV characteristics of materials such as Si, Graphene, InP, etc.  Up until this point I've been able to simulate the IV characteristics of Gold that show clear linear ohmic characteristic.  If anyone has done this previously in ATK, would you be able to direct me to a link or article or script on how to define properly a metal (possibly gold) - semiconductor - metal (possibly gold) structure and simulate its IV characteristics.

Thanks in advance.

7

General Questions and Answers / How to simulate a Silicon and InP sheet?

« on: March 16, 2012, 20:44 »

Hello and thank you for your attention.  I'm interested in simulating the I-V Characteristics of a 1nm wide by 2nm (nano ribbon ) long Silicon and InP structure. Once I repeat the unit cell of Si/InP, how do I convert the parallelogram created to a rectangle and define electrodes based on the shorter sides?

Thanks in advance.