ECE474S11_Lec18_23Feb11

ECE474S11_Lec18_23Feb11 - ECE 474: Principles of Electronic...

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ECE 474: Principles of Electronic Devices Prof. Virginia Ayres Michigan State University ayresv@msu.edu
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V.M. Ayres, ECE474, Spring 2011 Lecture 18: Vote: ± Shorter HW05 due Monday but no office hours ± Longer HW05 due Wednesday with office hours on Tuesday night 6:00-9:00 Vote result: Longer HW05 due Wednesday with office hours on Tuesday night 6:00-9:00. HW05 is now posted on the class website
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V.M. Ayres, ECE474, Spring 2011 Lecture 18: Chp. 03 ± Doping: it’s neutral ¾ Space charge neutrality ¾ When usual doping approximation is justified ¾ When it is not: temperature extremes ¾ When you choose not: co-doping ± Physical aspects of doping ± Drift Current Examples of each
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V.M. Ayres, ECE474, Spring 2011 Motivation: High power n-channel field effect transistor: Note 3 doped regions. Current I Ù I(n,p) n n p Wilkipedia
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V.M. Ayres, ECE474, Spring 2011 ( ) () 27) - (3 N p N n 25a) (3 exp n p 25a) (3 exp n n 24) - (3 n p n 20) (3 h kT m 2 π 2 (E) N 19) (3 exp N p 16a) (3 h kT m 2 π 2 (E) N 15) (3 exp N n d 0 - a 0 )/kT E E ( i 0 )/kT E E ( i 0 2 i 0 0 3/2 2 * h V /kT EV - E - V 0 3/2 2 * n C /kT E - E - C 0 F i i F F F C + + = + = = = = = = = Use these to analyze a doped semiconductor and find the carrier concentrations(n 0 , p 0 ) due to doping + temperature Minority Majority = e- OR Majority = holes Space charge neutrality
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V.M. Ayres, ECE474, Spring 2011 1. Carrier concentration is strongly a function of temperature: you are not always working at 300K. 2. You may choose co-doping: for carrier or for E F manipulation Use space charge neutrality to analyze these two situations N p N n d 0 - a 0 + + = +
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V.M. Ayres, ECE474, Spring 2011 3.33 @ 300K Temperature increases to left Partial “normal” doped lots of e- and o liberated by temperature alone dominate the concentrations at really high temps
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V.M. Ayres, ECE474, Spring 2011 Temperature example 01: Si is doped with 10 15 cm -3 P atoms. Over what temperature range does the approximation n 0 = N d = 10 15 cm -3 hold good?.
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V.M. Ayres, ECE474, Spring 2011
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ECE474S11_Lec18_23Feb11 - ECE 474: Principles of Electronic...

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