Chap.3-semicon-Handout

Chap.3-semicon-Handout - Chap.3 Semiconductors(5th ed...

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9/15/2011 1 Chap.3 Semiconductors ( 5 th ed: Sec.3.7-3.9 ) 1 2 Figure A.2 Conceptual illustration of a step-and-repeat reduction technique to facilitate the mass production of integrated circuits. i) Introduction Silicon is Semiconductor and is the basis material for Integrated Circuits 3 i) Introduction Silicon is Semiconductor and is the basis material for Integrated Circuits Figure A.1 Photolithography using positive or negative photoresist.
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9/15/2011 2 4 Figure A.5 A modern twin-well CMOS process flow with shallow trench isolation (STI). i) Introduction Silicon is Semiconductor and is the basis material for Integrated Circuits 5 Figure A.14 A CMOS inverter schematic and its layout. CMOS Inverter LAYOUT 6 Interactive animated applet for Nwell process for CMOS Inverter: http://jas.eng.buffalo.edu/education/fab/invFab/index.html LAYOUT : Cross-sectional View: CMOS IC Layout and Device Cross-section
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9/15/2011 3 PN Junction Diode 7 ii) Physical Operation of Diodes Anode Cathode sketch in 2D Sketch in 3D Outermost = 4 e’s Outermost = 8 e’s 2x2x2=8 unitcells Showing only the Ga and As atoms Single unitcell of GaAs 8 http://jas.eng.buffalo.edu/education/ solid/unitCell/home.html http://jas.eng.buffalo.edu/education/ solid/genUnitCell/750.html T=300K T=0K 9 Intrinsic = chemically pure material, without any chemical impurities. At T > 0 K, a few of those covalent bonds are broken. A broken covalent bond means that an electron, originally fixed within the bond, is now broken off from the bond and is set FREE to move around in the Si solid mobile Electron & Hole are generated. 3.1 Intrinsic Silicon
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9/15/2011 4 10 n = electron concentration p = hole concentration n = p = n i = intrinsic carrier concentration Answer) Assume that E g is indept. of Temperature ( which is only approximately true ) T=100K: n i = 7.3x10 15 ( 100 ) 3/2 exp[-1.12/(2*8.62x10 -5 * 100 )] = 7.3E18*e -64.965 = 4.46x10 -10 cm -3 3.1 Intrinsic Silicon n i = 1.5x10 10 cm -3 at T=300K, is a function of Temperature = B T 3/2 exp(-E g /2kT) where, B=material-dep. constant=7.3x10 15 cm -3 K -3/2 for silicon E g = Si bandgap energy = 1.12 eV for Si k = Boltzman’s const = 8.62x10 -5 eV/K Question) Find the intrinsic carrier density n i for silicon at T=100K and 400K T=400K: n i =7.3x10 15 *( 400 ) 3/2 *exp[-1.12/(2*8.62x10 -5 * 400 )]=5.84E19*e -16.24 = 5.16x10 12 cm -3 3.2 Doped Semiconductor: Extrinsic, n-type or p-type Donor Acceptor 11 n-type p-type n-type p-type 3.2 Doped Semiconductor: Extrinsic, n-type or p-type Donor Acceptor 12 n-type p-type
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9/15/2011 5 13 n-type : The donor impurity concentration dominates the intrinsic carrier concentration.
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