17 February 2010
Germanium nanoelectronics to replace silicon?
Research is underway on the use of germanium instead of silicon as the basic material of transistors which developers claim could enable faster chips containing smaller transistors.
Scientists at the Forschungszentrum Dresden-Rossendorf (FZD) say that Germanium is easily integrated into existing technological processes. It was the basic material of first generation transistors before it was replaced by silicon at the end of the 1960s.
By inserting foreign atoms, the conductivity of semiconductors can be varied, one possibility being annealing - ion implantation with subsequent heat treatment. Annealing of the germanium crystal is necessary as material is damaged during implantation. While these methods enabled the researchers to manufacture p-channel transistors, they were unable to produce corresponding n-channel transistors using germanium. This was because of the strong spatial redistribution of the phosphorous atoms which have to be used in manufacturing the n+ regions.
Physicists from FZD used a special annealing method which repaired the germanium crystal and yielded good electrical properties without the diffusion of phosphorus atoms. The germanium samples were heated by short light pulses of only a few milliseconds – a sufficient enough period to restore the crystal quality and to achieve electrical activation of phosphorus. However, it is too short for the spatial redistribution of the phosphorus atoms.
An alternative method to suppress phosphorus diffusion in germanium has been investigated by an international team of researchers across Europe and the USA, among them physicists from FZD. After ion implantation of phosphorus into germanium, the sample was heated and then irradiated by protons.
The results of these experiments revealed that in principle it is possible to fabricate germanium based n-channel transistors with dimensions corresponding to the most advanced technological requirements.
Author
Chris Shaw
Supporting Information
Websites
http://www.fzd.de
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