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Semiconductor_tutorial.pdf

Semiconductor_tutorial.pdf

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简介:本文档为《Semiconductor_tutorialpdf》,可适用于电子通讯领域,主题内容包含ProfessorNCheung,UCBerkeleySemiconductorTutorialEESEESemiconductorTutorial符等。

1Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 EE143 Semiconductor Tutorial -Electrons and “Holes” - Dopants in Semiconductors - Electron Energy Band Diagram - Mobility - Resistivity and Sheet Resistance 2Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 Why bother knowing Electrons and Holes ? Microfabrication controls dopant concentration distribution ND(x) and NA(x) Electron Concentration n(x) Hole Concentration p(x) Electrical resistivity Sheet Resistance Fermi level Ef (x) PN Diode Characteristics MOS Capacitor MOS Transistor Electric Field E(x) Effect Carrier Mobility 3Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 Electron Potential Energy Isolated atoms Atoms in a solid Available states at discreet energy levels Available states as continuous energy levels inside energy bands Conduction Band and Valence Band 4Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 5Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 The Simplified Electron Energy Band Diagram 6Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 Density of States at Conduction Band: The Greek Theater Analogy Plan View of the amphitheatre at Epidarus Electron Energy Amphitheatre at Epidarus, Greece. Built c350 BC. Energy Gap (no available seats) Note that the number of available seats at same potential energy increases with higher electron energy 7Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 An unoccupied electronic state in the valence band is called a “hole” Concept of a “hole” Conduction Band Valence Band 8Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 9Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 Electron and Hole Concentrations for homogeneous semiconductor at thermal equilibrium n: electron concentration (cm-3) p : hole concentration (cm-3) ND: donor concentration (cm-3) NA: acceptor concentration (cm-3) 1) Charge neutrality condition: ND + p = NA + n 2) Law of Mass Action : n p = ni2 Note: Carrier concentrations depend on NET dopant concentration (ND - NA) ! Assume completely ionized to form ND+ and NA - 10Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 How to find n, p when Na and Nd are known n- p = Nd - Na (1) pn = ni2 (2) (i) If Nd -Na > 10 ni : n º Nd -Na (ii) If Na - Nd > 10 ni : p º Na- Nd 11Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 Mobile charge-carrier drift velocity v is proportional to applied E-field: mn mp Carrier Mobility m | v | = m E Mobility depends on (ND + NA) ! (Unit: cm2/V•s) 12Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 R @ 2.6Rs Electrical Resistance of Layout Patterns (Unit of RS: ohms/square) L=1mm W = 1mm R = Rs R = Rs/2 R = 2Rs R = 3Rs 1m 1mR = Rs Metal contact Top View 13Professor N Cheung, U.C. Berkeley Semiconductor TutorialEE143 S06 RIC resistor = Rpaper RS resistor RS paper IC Resistor Pattern Resistor Paper Pattern microns centimeters magnified Resistance of Arbitrary Layout Patterns Before you do the layout and fabricate the structure which is expensive and time consuming. Cut out a similar pattern on a resistor paper with a known RS paper Measure Rpaper experimentally across the two terminals You know RS resistor of of a microfabricated layer by 4-point probe method. Will this layout pattern give the desired R value ? You can deduce

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