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Why are impurities deliberately added to silicon used in integrated circuits?
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crystal
A crystal form of elemental sulfur. Sulfur has an atomic weight of about 32.06 atomic mass units (amu), which means that its molar mass is 32.06 grams.
Pure silicon is a semiconductor that, in its intrinsic crystalline state, has a very high resistance to electrical current at room temperature. To make silicon useful for integrated circuits, impurities are deliberately added through a process called doping to modify its electrical conductivity.123
By introducing specific dopant atoms, engineers can create two types of semiconductors:
- n-type: Adding elements with more outer electrons than silicon (such as phosphorus or arsenic) provides excess free electrons that act as negative charge carriers.124
- p-type: Adding elements with fewer outer electrons (such as boron) creates "holes" in the crystal lattice, which function as mobile positive charge carriers.124
This controlled doping allows silicon to function as a switch, turning current on and off as needed. Furthermore, creating junctions between these two layers enables the formation of p-n junctions, which are essential for rectifying current and building the transistors that power modern electronic devices.14