lec_2.4 - 2.4 Carrier Generation Recombination Perturbation...

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ECE3080, Chapter 2.4 1 May 30, 2005 ECE 3080: Chapter 2.4 – Device Fundamentals O. Brand, 1 of 20 2.4 Carrier Generation & Recombination Perturbation of semiconductor, i.e. an excess or deficit in carrier concentration with respect to the equilibrium values is created, resulting in non-equilibrium conditions 2.4.1 Generation and Recombination Processes 2.4.2 Direct or Band-to-Band Recombination/Generation 2.4.3 Indirect or R-G Center Recombination/Generation 2.4.4 Continuity Equations Literature: Pierret, Chapter 3.3-3.5.1, page 105-132 Sze, Chapter 3, page 47-83 May 30, 2005 ECE 3080: Chapter 2.4 – Device Fundamentals O. Brand, 2 of 20 2.4.1 Carrier Injection/Generation Processes: Photogeneration Operation of diode in forward direction Impact ionization p n > n i 2
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ECE3080, Chapter 2.4 2 May 30, 2005 ECE 3080: Chapter 2.4 – Device Fundamentals O. Brand, 3 of 20 Carrier Extraction/Recombination Processes: Operation of diode in reverse direction Auger recombination: band-to-band recombination which occurs simultaneously with collision between two like carriers (can be important in highly-doped direct bandgap semiconductors) p n < n i 2 May 30, 2005 ECE 3080: Chapter 2.4 – Device Fundamentals O. Brand, 4 of 20 Carrier Generation/Recombination After switching off the distortion, the system returns to the equilibrium state (p n = n i 2 ) with a characteristic time constant, i.e. excess carriers will recombine (in case p n > n i 2 ) or additional carriers will be generated (in case p n < n i 2 ) Notation: n n electron density in n-type semiconductor p n hole density in n-type semiconductor n n0 , p n0 equilibrium carrier densities n p electron density in p-type semiconductor p p hole density in p-type semiconductor n p0 , p p0 equilibrium carrier densities
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ECE3080, Chapter 2.4 3 May 30, 2005 ECE 3080: Chapter 2.4 – Device Fundamentals O. Brand, 5 of 20 Low-Level/High-Level Injection Low-Level Injection: High-Level Injection: ! n = ! p << N D n n = n n0 + ! n " n n0 p n = p n0 + ! p " ! p < n n0 ! n = ! p " N D n n = n n0 + ! n > n n0 p n = p n0 + ! p # ! p > n n0 Example: Injection by photogeneration ( Δ n = Δ p) in n-type
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