MIT6_012S09_lec05

MIT6_012S09_lec05 - Lecture 5 PN Junction and MOS...

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Lecture 5 PN Junction and MOS Electrostatics(II) PN JUNCTION IN THERMAL EQUILIBRIUM Outline 1. Introduction 2. Electrostatics of pn junction in thermal equilibrium 3. The depletion approximation 4. Contact potentials Reading Assignment: Howe and Sodini, Chapter 3, Sections 3.3-3.6 6.012 Spring 2009 Lecture 5 1
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1. Introduction pn junction p-region and n-region in intimate contact Why is the p-n junction worth studying? It is present in virtually every semiconductor device! Example: CMOS cross-section Understanding the pn junction is essential to understanding transistor operation 6.012 Spring 2009 Lecture 5 2 p n n + n + n + p + p + p + p-MOSFET n-MOSFET Figure by MIT OpenCourseWare.
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Doping distribution of an abrupt p-n junction 2. Electrostatics of p-n junction in equilibrium Focus on intrinsic region: 6.012 Spring 2009 Lecture 5 3
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What is the carrier concentration distribution in thermal equilibrium? First think of the two sides separately: Now bring the two sides together. What happens? 6.012 Spring 2009 Lecture 5 4
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Resulting carrier concentration profile in thermal equilibrium: Far away from the metallurgical junction: nothing happens Two quasi-neutral regions Around the metallurgical junction: diffusion of carriers must counter-balance drift Space-charge region 6.012 Spring 2009 Lecture 5 5
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On a linear scale: Now, we want to know n o (x), p o (x), ρ (x), E(x) and φ (x).
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MIT6_012S09_lec05 - Lecture 5 PN Junction and MOS...

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