ExtraNotesOnExtrinsicSemiconductors

ExtraNotesOnExtrinsicSemiconductors - Extrinsic...

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EMS 172 – Extra Notes on Semiconductors Extrinsic Semiconductors - Intentional impurities called dopants are added to alter the electrical properties n-type silicon : dopants are donor atoms that have an extra electron compared to the semiconductor host to give up (donate) to the conduction band; the dopant atom becomes ionized when it donates the electron therefore taking on a (+)ve charge; only a small energy (E C -E D ) is needed to ionize the dopant atom; (E C -E D ) is almost the binding energy of the extra electron. Freeze out regime – only some dopants are ionized = = + T k E E N N N N B D C D c D e 2 exp 2 1 2 1 ; N D + is the concentration of ionized donor atoms (atoms/cm 3 ) Si E Conduction band Valence band Bandgap Ev=0 Ec=Eg E Ev=0 Ec=Eg F(E) E F 1 E Z(E) N(E) E electrons E D E F E D holes E CB VB Ev=0 Ec=Eg E D E F T = 0K E T > 0K Freeze Out E T >> 0K Extrinsic E T >>>> 0K Intrinsic Si Si Si Si Si Si Si Si Si
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ExtraNotesOnExtrinsicSemiconductors - Extrinsic...

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