Homework3_Solution

Homework3_Solution - ECE 3040 Dr. Alan Doolittle...

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ECE 3040 Dr. Alan Doolittle Microelectronic Circuits Homework #3 NOTE: Some reference materials including tables, figures etc. .. handed out in class or in your text may be needed to solve these problems. 1.) Pierret 3.2 parts “c” and “d”.
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ECE 3040 Dr. Alan Doolittle Microelectronic Circuits 2.) Pierret 3.6
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ECE 3040 Dr. Alan Doolittle Microelectronic Circuits 3.) Pierret 3.13
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ECE 3040 Dr. Alan Doolittle Microelectronic Circuits 4.) A 2 ohm-cm p-type silicon bar with an electron mobility of 1000 cm 2 /VSec and hole mobility of 250 cm 2 /VSec is to be used as a photoconductor (a device that has it’s resistivity change with illumination). The bar is 10 cm long and has a cross sectional area of 0.1 cm 2 . A.) What is the resistance of the bar? R=( ρ L)/A = 2(10)/0.1= 200 ohms B.) What is the electron and hole concentrations in the bar? Assume that the resistivity does not depend on the electron concentration (N A >>N D and N A >>n i ): ρ =1/(q µ N A ) ==> p=N A = 1/(2 x 1.6e-19 x 250 ) = 1.25e16 cm -3 n=(n i ) 2 /p = (1e10) 2 /1.25e16 = 8000 cm -3 Verify that the resistivity is not dependent on the electron concentration: ρ =1/(q µ p p + q µ n n) =1/(1.6e-19(250 x 1.25e16 + 1000 x 8000))=2 ohm-cm C.) If light generates 10 16 cm -3 electrons in steady state, assuming no change in mobility, what is the new resistance of the bar? ρ =1/(q µ p (p o + p) + q µ n (n o + n)) =1/(1.6e-19(250 x (1.25e16 +1e16)+ 1000 x (1e16+8000))) = 0.4 ohm-cm R=( ρ L)/A = 0.4(10)/0.1= 40 ohms D.) It is desired to have a SIMPLE circuit that will read the change in resistance. You only have at your disposal a 9 volt battery, another 4 ohm resistor, wire and a voltmeter.
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Homework3_Solution - ECE 3040 Dr. Alan Doolittle...

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