3. The semiconductor material silicon

Semiconductors are widely used in familiar electric appliances such as personal computers, televisions, smartphones, digital cameras, IC cards, etc. The material most frequently used in semiconductors is Silicon (chemical symbol = Si). Silicon is the second most abundant element on earth after Oxygen. Most Silicon is found in soil and rock, but Silicon is also contained in natural water, trees and plants.
In nature, however, Silicon is found in the form of compounds with Oxygen, Aluminum and Magnesium. As a result, the Silicon element must be extracted from the compound and purified. Silicon used in a semiconductors such as an integrated circuits (IC) requires a single crystal structure of ultra-high-purity &#;99.%&#; (the so-called &#;eleven nines&#;) and is refined using various processes after extraction.
A single crystal structure is a structure whereby atoms are arranged in an orderly fashion in three dimensions, and the basic unit of the arrangement is called the crystal lattice. A single crystal is a crystal lattice in an orderly, continuous arrangement. A Silicon crystal lattice has a diamond cubic crystal structure in a repeating pattern of eight atoms. Each Silicon atom is combined with four neighboring silicon atoms by four bonds. Silicon, a very common element, is used as the raw material of semiconductors because of its stable structure.
Purification of Silicon consumes large amounts of power. In Japan, refined Silicon (ingot) with purity of at least 98% is imported from Australia, China and Brazil, where electricity is relatively inexpensive.

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Transcript

NARRATOR: These mountains hold a substance that could make the production of solar energy much more economical in the future. The Tana quarry in Norway, near the North Cape - here quartz is mined. Mineral quartz is 99 percent silicon, one of the most important raw materials of the 21st century. Silicon is in every computer, mobile and, of course, in solar cells. Trond Brendan-Veisal is a geologist. He is searching for rock particularly free from impurities.

TROND BRENDAN-VEISAL: "If the raw materials we are using is clean enough we don't have to think about all the cleaning processes after the production of the metalurgical silicon. That means that the cost probably could drop considerably."

NARRATOR: Although the silicon in the rock is highly concentrated, it still needs to undergo a costly and energy-intensive purification process before it can be used industrially.

In this plant in Kristiansand the clean quartz is processed into high-purity silicon. The rock is melted in a furnace at 4,000 degrees and the silicon purified even further. The process itself is similar to that used in steel production and is why this molten rock is often referred to as metallurgical silicon. Yet the physical properties are not like those of a metal, they are instead like those of a semiconductor. The electrical conductivity of this material can be specifically altered by adding minute amounts of other substances. These characteristics are critical in determining the silicon's ability to perform efficiently in solar cells. At the end of the purification process, the resulting metallurgic silicon has a purity of 99. percent.

BRENDAN-VEISAL: "It's quite exciting, actually, to have this ingot in my hand here because I have found the quartz and I have followed the quartz from the mine to the plant and now to this final product."

NARRATOR: Here in the Arctic Circle there are deposits of pure silicon used for generating solar power. And this is a place where, for two months a year, the sun never even shines.

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