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QuantumATK => General Questions and Answers => Topic started by: Ash on June 11, 2012, 06:17

Title: Physical significance of Device Density of States (DDOS) ?
Post by: Ash on June 11, 2012, 06:17

Hi everyone,
Can anyone tell me the interpretation of the DDOS, is the result of the DOS alignment between electrodes and central region at different biases or just the DOS of the entire device. Why does it vary with respect to the gate or electrodes biases?
Can it DDOS be used for the explanation of the I-V characteristics other than Transmission spectrum?

Title: Re: Physical significance of Device Density of States (DDOS) ?
Post by: Ash on June 12, 2012, 15:22

I would really appreciate your answers and suggestions.  :)

Title: Re: Physical significance of Device Density of States (DDOS) ?
Post by: zh on June 13, 2012, 07:41

By default, the zero of energy in the device DOS is set to the average of the Fermi Levels of the left and right electrodes, and the device DOS is just for the center region.
http://quantumwise.com/documents/manuals/latest/ReferenceManual/XHTML/ref.devicedensityofstates.html

When the gate voltage or electrode bias voltages are applied, the device DOS should change with the applied voltage due to the charge injection of gate or the shifting of the Fermi levels in two electrodes.  It is sure that the device DOS can be used to explain the I-V curve or the transmission spectrum. But it is not alway obvious.

Title: Re: Physical significance of Device Density of States (DDOS) ?
Post by: Ash on June 13, 2012, 08:46

Are you certain at the point that device DOS is just for scattering or center region and not for the device I tried to find this in the reference that you gave me (http://quantumwise.com/documents/manuals/latest/ReferenceManual/XHTML/ref.devicedensityofstates.html (http://quantumwise.com/documents/manuals/latest/ReferenceManual/XHTML/ref.devicedensityofstates.html)). However, I could not find it anywhere mentioned. If it is the case, that would be answer to my other question that I posted on the forum (http://quantumwise.com/forum/index.php?topic=1645.msg8137;topicseen#msg8137 (http://quantumwise.com/forum/index.php?topic=1645.msg8137;topicseen#msg8137)).
Also, why the application of either the gate or electrodes voltage changes the amplitude of DDOS peaks. I thought it just shifts the DOS peaks in energy?

Title: Re: Physical significance of Device Density of States (DDOS) ?
Post by: Anders Blom on June 13, 2012, 13:45

The DOS computed for a device configuration is indeed the device DOS, but it's computed for the atoms in the central region (with device boundary conditions, not bulk), i.e. the electrodes (which are bulk) are not included.

The magnitude of the DOS depends quite strongly on the k-point and energy sampling. The peaks are often quite sharp, so when they move a little bit due to the gate, your sample point (in energy) may end up on different points of the peak. The effect should go away to some extent with a higher k-point sampling and denser energy points, however not completely, it is also expected that there is some changes in the electronic states due to the gate, so part of the amplitude can be due to that.

Title: Re: Physical significance of Device Density of States (DDOS) ?
Post by: Ash on June 13, 2012, 17:32

Thanks Zh and Blom for your invaluable replies !!