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Doping Scheme of Semiconducting Atomic Chain

Toshishige Yamada*

MRJ, NASA Ames Research Center

This is an abstract for a talk to be given at the Fifth Foresight Conference on Molecular Nanotechnology. There will be a link from here to the full article when it is available on the web.

Due to the dramatic reduction in device size down to 0.1 micrometers, electrons start to see a few dozens of discrete dopant atoms randomly scattered in the channel. The characteristics may be different among the transistors that are designed to be the same, and this places a serious limitation for integration. A fundamental solution is to create electronics with atomically precise elements, which could be fabricated with atom manipulation technology. Atomic chain electronics belongs to this category. Foreign atoms are placed to form chains on an atomically regulated substrate surface. Using the tight-binding theory with universal parameters, it has been predicted that Si chains are metallic and Mg chains are insulating, regardless of the lattice constant [1].

For electronic applications, it is essential to establish a method to dope a semiconducting chain, which is to control the Fermi energy position without altering the original band structure. If we replace some of the chain atoms with dopant atoms randomly, the electrons will see random potential along the chain and will be localized strongly in space (Anderson localization). However, if we replace periodically, although the electrons can spread over the chain, there will generally appear new bands and band gaps reflecting the new periodicity of dopant atoms. This will change the original band structure significantly. In order to overcome this dilemma, we may place a dopant atom beside the chain at every N lattice periods (N >> 1). Because of the periodic arrangement of dopant atoms, we can avoid the unwanted Anderson localization. Moreover, since the dopant atoms do not constitute the chain, the overlap interaction between them is minimized, and the band structure modification can be made smallest. Some tight-binding results will be discussed to demonstrate the present idea.

[1] T. Yamada, Y. Yamamoto, and W. A. Harrison, J. Vac. Sci. Technol. B 14, 1243 (1996); T. Yamada, ibid B 15, 1019 (1997).

*Corresponding Address:
Dr. Toshishige Yamada
NASA Ames Research Center, Mail Stop T27A-1
Moffett Field, CA 94035-1000
telephone: (650) 604-4333; fax: (650) 604-3957
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