MIT6_012S09_lec14

MIT6_012S09_lec14 - Lecture 14 The pn Junction Diode (I) IV...

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Lecture 14 The pn Junction Diode (I) I-V Characteristics Outline pn junction under bias IV characteristics Reading Assignment: Howe and Sodini; Chapter 6, Sections 6.1-6.3 6.012 Spring 2009 Lecture 14 1
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1. PN junction under bias Focus on intrinsic region: meKd contact to p dde l(~dL metd contact to n side Upon application of voltage: Electrostatics upset: - depletion region widens or shrinks Current flows - With rectifying behavior Carrier charge storage 6.012 Spring 2009 Lecture 14
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I-V Characteristics 0.25 0 0.50 0.75 V D (V) I D ( µ A) 0.25 18 19 20 100 200 300 100 200 (a) (b) V D (mV) I D ( µ A) (log scale) 500 550 600 650 700 750 10 2 0.1 1 10 100 10 3 800 slope q kT V BD Forward Bias Reverse Bias Breakdown To model I-V characteristics we need 2 concepts The Law of the Junction Steady-State Diffusion 6.012 Spring 2009 Lecture 14 3
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Carrier Profiles: in thermal equilibrium In equilibrium: dynamic balance between drift and diffusion for electrons and holes inside SCR. J drift = J diff ln p o , n o p o n o N d n i 2 N d x 0 N a n i 2 N a J h diff J h drift J e diff J e drift 6.012 Spring 2009 Lecture 14 4
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Carrier Profiles: under forward bias Current balance in SCR broken: J drift < J diff For V>0, φ B - V ↓ ⇒ |E SCR | ↓ ⇒ |J drift | Net diffusion current in SCR minority carrier injection into QNRs. Carrier flow can be high because lots of minority carriers are injected into QNRs from the majority side. ln p, n p o p n o n N d n i 2 N d x 0 N a n i 2 N a J h diff J h J e J h drift J e diff J e drift 6.012 Spring 2009 Lecture 14 5
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Carrier Profiles: under reverse bias Current balance in SCR broken: J drift > J diff For V<0, φ B - V ↑ ⇒ |E SCR | ↑ ⇒ |J drift | Net drift current in SCR minority carrier extraction from QNRs. Carrier
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This note was uploaded on 11/07/2011 for the course COMPUTERSC 6.012 taught by Professor Charlesg.sodini during the Spring '09 term at MIT.

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MIT6_012S09_lec14 - Lecture 14 The pn Junction Diode (I) IV...

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