lec9 - ENGR 111 Lecture 11 Reading: Chapters 25,27 Class...

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ENGR 111 Lecture 11 Reading: Chapters 25,27 Class notes,hyperlinked websites
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Review of last lecture z Metals conduct electricity at room temperatures z Insulators do not conduct electricity z Semiconductors are in between { Normally not-conductive, but can be made to conduct { They can be “doped” to conduct electricity
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What’s the difference? z The electrons are in two bands, valence band and conduction band Insulator Semiconductor Metal Conduction band Valence band
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Semiconductors z Not many free electrons, normally z Add dopants { Silicon has 4 electrons in outer shell { Dopants are with either 3 or 5 electrons { N-type has electrons as carriers { P-type has holes as carriers
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n-type and p-type semiconductors z Valence and conduction bands N-type electrons as conductors P-type holes as conductors Donor energy level Acceptor energy level
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n-p junctions z A depletion zone prevents normal flow of carriers z Forward bias enables current flow z Reverse bias –no current flow z Current flows in one direction
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p-n junction (voltage-current) V d = 0.7 V for silicon diodes
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lec9 - ENGR 111 Lecture 11 Reading: Chapters 25,27 Class...

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