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| Volume 9, Number 1 | August 10, 2001 |
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Physicist working to create diamond-based semiconductors
By Elizabeth Frogley Faster, smaller and more powerful computer chips could one day be made with diamonds, says a University of Saskatchewan physicist who hopes to be the first to synthesize diamond-based semiconductors. "Diamond is an ideal material for microelectronics," says Akira Hirose, explaining that diamond’s high thermal conductivity could make possible computer chips one-tenth the size of current silicon chips. "If successful, this will revolutionize the electronics industry." But these tiny diamond semiconductors can’t yet be produced because the type of diamond needed – ‘n-type’ diamonds – does not yet exist. Transistors used in electronics and computer chips require both ‘n-type’ and ‘p-type’ semiconductors. N-type semiconductors have mobile electrons that carry electrical current, while p-type semiconductors have electron deficiencies or holes that act as carriers of electrical current. P-type diamonds are readily available in nature as impure diamonds, but n-type diamonds would have to be synthesized in the lab. 
In April, Hirose was awarded a Canada Research Chair in Plasma Science, which provides $1.4 million over seven years for research on plasma-based materials science. His main focus is on producing n-type diamonds using a plasma reactor. As a first step to making diamond-based semiconductors, Hirose’s team has recently synthesized pure diamonds. These are poor conductors, but the team hopes to create n-type, current-carrying diamonds by adding impurities, a process called ‘doping.’ This would be similar to the way silicon is doped with arsenic to create the n-type silicon semiconductors currently in use. Plasma-based synthesis and modification of materials is an emerging technology that uses high temperatures to create or speed up chemical reactions that wouldn’t usually occur, says Hirose. With $410,000 from the Canada Foundation for Innovation, Hirose and his team (two other professors, a post-doctoral research fellow, a research engineer, and about half a dozen graduate students) are building new plasma reactors for plasma-based materials science. Plasma, a unique state of matter in which there are roughly equal numbers of positively and negatively charged particles, can be composed of any material. A substance is heated to 10,000 degrees Celsius until negatively charged electrons are knocked free from neutral atoms or molecules. Particles can then be manipulated into arrangements they would not normally form, like the crystalline structure of a diamond. To make pure diamonds, Hirose’s team heated hydrogen and methane into plasma in a plasma reactor built specifically for diamond synthesis. Methane contains the carbon atoms that form the diamonds. Specially designed discharge tubes provide the right environment for the carbon atoms to assemble into a crystalline structure and form diamond grains. Diamond grains synthesized using plasma technology are too small for commercial use in jewelry, but Hirose says that with continued research and technological refinement, larger ones could be created. Artificial diamonds could also be used in manufacturing products like wear-resistant cutting tools or optical components such as lenses. His lab has also used plasma reactors to make "carbon nano-tubes" – carbon-based molecules that can carry a current. These molecular wires are as tiny as 10 nanometres in diameter (a nanometre is one-billionth of a metre), much smaller than the miniaturized transistors used in silicon chips. With the help of the Canadian Light Source synchrotron at the U of S, Hirose hopes to be able to further study electron conduction and create a molecular wire that is 1,000 times as strong as a steel wire which could be used, for example, in advanced electron microscopes. It’s all part of the race to create ultra-miniaturized semiconductors. "It is difficult to tell when we can achieve n-type diamond semiconductors, if at all," says Hirose. "It is high-risk research, but with an enormous payoff if successful."
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