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Electronics >> Basics of Electronics >> Silicon


What is Silicon?

Silicon, atomic number 14 on the periodic table, is a semiconducting material from which integrated circuits (computer chips of all types--processors, memory chips, etc.; CCDs; transistors; etc.) are created.

Silicon is one of the most common elements on Earth in the Earth's crust, it's second in mass only to oxygen and can be found in any quartz crystal. Beach sand is largely silicon. Silicon is also the semiconductor material out of which almost all modern transistors are made.

How is Semiconductor made from Silicon?

Semiconductor devices are made primarily of silicon ("Si").

Pure silicon forms rigid crystals because of its four valence (outermost) electron structure - one Si  atom bonds to four other Si atoms forming a very regularly shaped diamond pattern. 

Pure silicon is not a conductor because there are no free electrons; all the electrons are tightly bound to neighboring atoms.

To make silicon conducting, producers combine or "dope" pure silicon with very small amounts of other elements like boron or phosphorus. Phosphorus has five outer valence electrons. When three silicon atoms and one phosphorus atom bind together in the basic silicon crystal cell of four atoms, there is an extra electron and a net negative charge.

This type of material is called n-type silicon. The extra electron in the crystal cell is not strongly attached and can be released by normal thermal energy to carry current; the conductivity depends on the amount of phosphorus added to the silicon.

Boron has only three valance electrons. When three silicon atoms and one boron atom bind with each other there is a "hole" where another electron would be if the boron atom were silicon. This gives the crystal cell a positive net charge (referred to as p-type silicon), and the ability to pick up an electron easily from a neighboring cell.

The resulting migration of electron vacancies or holes acts like a flow of positive charge through the crystal and can support a current. It is sometimes convenient to refer to this current as a flow of positive holes, but in fact the current is really the result of electrons moving in the opposite direction from vacancy to vacancy.

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