ECE331 Wi11 lecture 7

ECE331 Wi11 lecture 7 - Chapter 5: Diffusion in Solids...

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Unformatted text preview: Chapter 5: Diffusion in Solids ISSUES TO ADDRESS... How does diffusion occur? How does diffusion occur? Why is it an important part of processing? How can the rate of diffusion be predicted for some simple cases? How does diffusion depend on structure and temperature? Chapter 5 - 1 Diffusion Diffusion- Mass transport by atomic motion Mechanisms Gases & Liquids random (Brownian) motion olids acancy diffusion or interstitial diffusion Solids vacancy diffusion or interstitial diffusion Chapter 5 - 2 Diffusion Interdiffusion : In an alloy, atoms tend to migrate from regions of high conc. to regions of low conc. Initially dapted from After some time Adapted from Figs. 5.1 and 5.2, Callister 7e . Chapter 5 - 3 Diffusion Self-diffusion : In an elemental solid, atoms also migrate. Label some atoms After some time C C A D A D B B Chapter 5 - 4 Diffusion Mechanisms Vacancy Diffusion: atoms exchange with vacancies atoms exchange with vacancies applies to substitutional impurities atoms rate depends on: umber of vacancies--number of vacancies--activation energy to exchange. Chapter 5 - 5 increasing elapsed time Diffusion Mechanisms Interstitial diffusion smaller atoms can iffuse between atoms diffuse between atoms. Adapted from Fig. 5.3 (b), Callister 7e . Chapter 5 - 6 More rapid than vacancy diffusion Processing Using Diffusion Adapted from chapter-opening Case Hardening :--Diffuse carbon atoms photograph, Chapter 5, Callister 7e. (Courtesy of Surface Division, idl d ) into the host iron atoms at the surface.--Example of interstitial Midland-Ross.) diffusion is a case hardened gear. Result: The presence of C Result: The presence of C atoms makes iron (steel) harder. Chapter 5 - 7 Processing Using Diffusion Doping silicon with phosphorus for n-type semiconductors: Process: 0.5um 1. Deposit P rich layers on surface....
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This note was uploaded on 04/30/2011 for the course ECE 331 taught by Professor Rajan during the Spring '09 term at Ohio State.

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ECE331 Wi11 lecture 7 - Chapter 5: Diffusion in Solids...

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