Single-crystal Silicon

Single-Crystal Silicon
To creat a silicon in a single-crystal state,we must first melt high-purity silicon.we then cause it to reform or solidify very slowly in contact with a single crystal"seed" the silicon adapts to the pattern of the single-crystal seed as it cools and gradually solidifies.Not surprisingly,because we start form a seed,we say this process is "growing"a new rod (often called a "boule") of single-crystal silicon out of molten silicon.Several different processes can be used to grow a boule of singly-crystal silicon .The most established and dependable processes are the Czochralski (Cz) method and the float-zone(Fz)techique .we also discuss"ribbon-growth" techniques.

Czochralski Silicon
In the Czochralski process, a seed crystal is dipped into a crucible of molten silicon and withdrawn slowly,pulling a cylindrical single crystal as the silicon crystallines on the seed.

Float-zone Silicon
The float-zone process produces purer crystals than the Czochralski method, because they are not contaminated by the crucible used in growing Czochralski crystal .In the float-zone process , a silicon rod is set atop a seed crystal and then field induces an electric field in the rod .Heating and melting the inerface between the rod and the seed.Single-crystal silicon forms at the interface.Growing upward as the coils are slowly raised.

Once the single-crystal rods are produces ,by either the Cz or Fz method, they must be sliced or sawn to form this wafers.Such sawing ,however ,wasters as much as 20% of the valuable silicon as sawdust ,known as"kerf" .The resulting thin wafers are then doped to produce the necessary electric field .They are then treated with a coating to reduce reflection, and coated with electrical contacts to form functioning Pv Cells.