Extrinsic Semiconductors. ECE 2204. Definitions. Intrinsic Pure There are an equal number of electrons and holes Extrinsic Contains impurities (donors, acceptors, and traps) The material properties are dominated by the concentration of the impurities and their effect on the crystal - PowerPoint PPT Presentation
Extrinsic SemiconductorsECE 2204DefinitionsIntrinsicPureThere are an equal number of electrons and holesExtrinsicContains impurities (donors, acceptors, and traps)The material properties are dominated by the concentration of the impurities and their effect on the crystalUsually, n pBack to the Periodic Table
Column V AtomsHave 5 outer shell electrons
The extra electron on the phosphorous atom is easily removed and becomes a free electron without generating a hole. The phosphorous atom becomes positively charged (ionized).Back to the Periodic Table (again)
Column III AtomsHave 3 outer shell electrons
Missing outer shell electron when compared to Si
The gallium atom steals an electron from a neighboring Si atom to complete the four bonds with the surrounding Si atoms, generating a hole at the neighboring Si atom. The boron atom becomes negatively charged (ionized).n-type SemiconductorsAre doped with donor atoms, which have an extra electron that they donate to the crystalWhen the concentration of donor atoms is much greater than the intrinsic carrier concentration, the electron concentration is composed of these donated electrons.
p-type SemiconductorsAre doped with acceptor atoms, which generate holes in the crystalWhen the concentration of acceptor atoms is much greater than the intrinsic carrier concentration, the hole concentration is composed of the holes generated by the acceptors.
Minority Carrier Concentrations
n-type semiconductorp-type semiconductor
n-type semiconductorp-type semiconductor13Temperature EffectsUnfortunately, the simplification of the equation for resistivity gets rid of its temperature dependence of the resistivity. Why? (Always blame the intrinsic carrier concentration for temperature effects it is usually the cause.)