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Chapter 3 Diodes3 - /2/12 Chapter 3 Diodes Physical...

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S J T U J. C h e n 1 3/2/12 Physical Operation of Diodes Chapter 3 Diodes
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3/2/12 SJTU J. Chen 2 Width of the Depletion Region: Depletion region exists almost entirely on the slightly doped side. Width depends on the voltage across the junction. Width of the depletion region o D A depo V N N q W ) 1 1 ( 2 + = ε ) ) 1 1 ( 2 V V N N q W o D A dep + = ε
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3/2/12 SJTU J. Chen 3 The diode i– v relationship with some scales expanded and others compressed in order to reveal details I-V Characteristics
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3/2/12 SJTU J. Chen 4 The Forward-Bias Region, determined by The Reverse-Bias Region, determined by The Breakdown Region, determined by Terminal characteristic of junction diodes o v 0 < < - v V ZK ZK V v - <
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3/2/12 SJTU J. Chen 5 Ø The pn junction excited by a constant- current source supplying a current I in the forward direction. Ø The depletion layer narrows and the barrier voltage decreases by V volts, which appears as an external voltage in the forward direction. The pn junction under forward-bias ----
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3/2/12 SJTU J. Chen 6 Carrier distribution under forward-bias Minority-carrier distribution in a forward- biased pn junction. It is assumed that the p region is more heavily doped than the n region; NA >> ND .
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3/2/12 SJTU J. Chen 7 Excess minority carrier concentration where excess-minority-carrier lifetime Ø Exponential relationship Ø Small voltage incremental gives rise to great incremental of excess minority carrier concentration diffusion length law of the junction n p p n L x x p p p p p L x x n n n no n e n x n n x n e p x p p x p ) ( 0 0 ) ( 0 ] ) ( [ ) ( ] ) ( [ ) ( - - + = - + = - , p p p n n n L D L D τ τ = = p n τ τ , 0 0 ( ) , ( ) T T v v V V n n n p p p p x p e n x n e = - =
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3/2/12 SJTU J. Chen 8 Total current under forward-bias where Is ---saturation current A ---junction cross-sectional area 0 0 2 ( ) ( ( ) ( ) ( )( 1) ( )( 1) ( 1) n p T T T pD nD pD nD x x x x V V p n n p p V V n i p n p D n A V V s dp x dn x I I I A J J A q q dx dx D p D n D D qA e qAn e L L L n L n I e ) = =- = + = + = - + = + - = + - = -
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3/2/12 SJTU J. Chen 9 Ø
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