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Posted: May 29, 2014

A Wigner based TCAD tool for the design of single dopant devices

(Nanowerk Spotlight) As we are approaching the post-CMOS area, device architectures that are drastically different from today's semiconductor chips are being proposed by researchers. New design concepts are now focused on devices that have not to work despite the presence of quantum effects, but because of them.
Solotronics is a relatively new field of optoelectronics that aims to exploit quantum effects at the ultimate limits of miniaturization. This technology seeks to provide a possibility to create in a controllable manner – and to manipulate – single dopants in solids in order to develop optoelectronic devices with only one dopant. To do that, it addresses single dopants placed in a semiconductor material with atomic precision.
Experiments are advancing quite quickly showing that this new approach could eventually lead to novel computer memories, on-demand photon sources, and even quantum computing.
"While experiments are showing quite exciting results, the theoretical comprehension of the phenomena happening at that scale is in its infancy," Dr. Jean Michel Sellier, a scientists at the Institute of Information and Communication Technologies (IICT) of the Bulgarian Academy of Sciences in Sofia, tells Nanowerk. "Indeed, it requires an approach that should be time-dependent (it is not known if a stationary regime can be found in these new devices), full quantum (at that scale the particle-wave duality is very pronounced) and should be able to include the effects due to the lattice vibrations – in other words, the effects due to the temperature have to be included for a reliable TCAD (Technology Computer Aided Design) tool."
Sellier adds that, from this perspective, the Wigner formalism of quantum mechanics has shown to be a very good approach: "It is time-dependent, full quantum and can include (yet at a phenomenological level) the effects of the temperature."
This video shows the time-dependent evolution of a 3D Gaussian wave packet interacting with the potential due to a phosphorus dopant atom in a silicon device. The initial energy for the electron is 0.42eV. No potential is applied. The lattice temperature is 300K. This device represents a candidate for quantum computers based on silicon. The calculations are obtained by using the Wigner-Boltzmann Monte Carlo method.
Using their novel approach, Sellier and Dimov are able to show the evolution of a wave packet in proximity of a phosphorus dopant at different temperatures. In particular, they have shown how the evolution can be strongly affected by the lattice vibrations of the host material at room temperature.
Sellier points out that this is a very exciting approach. "It may eventually be used as a practical TCAD tool for realistic design of solotronic devices. This could eventually lead to realistic quantum computing device design."
Sellier and Prof. Ivan Dimov, also from the IICT, have now published a paper in Computer Physics Communications ("The Wigner-Boltzmann Monte Carlo method applied to electron transport in the presence of a single dopant"), showing for the first time a three-dimensional, time-dependent application of the Wigner formalism to a realistic case concerning a single dopant (phosphorus) embedded in a semiconductor material (silicon).
For more information about their new approach and simulator (nano-archimedes) readers may have a look at the nano-archimedes website.
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