lecture11

# lecture11 - 6.720J/3.43J Integrated Microelectronic Devices...

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Unformatted text preview: 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 11-1 Lecture 11 - Carrier Flow (cont.) March 1, 2007 Contents: 1. Dynamics of majority-carrier-type situations 2. Dynamics of minority-carrier-type situations Reading assignment: del Alamo, Ch. 5, §§ 5.4 Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 11-2 Key questions • What is the characteristic time constant of majority-carrier-type stuations? • What is the characteristic time constant of minority-carrier-type situations? Always? Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 11-3 1. Dynamics of majority-carrier-type situations Continuity equation for net volume charge: ∂J t ∂ρ = − ∂x ∂t Under static conditions: ∂ρ = 0 ⇒ ∂J t = 0 ⇒ J t uniform in space ∂t ∂x Under dynamic conditions: ∂ρ = 0 ⇒ charge redistribution ∂t ⇒ ∂J t = 0 ⇒ charge ﬂow ∂x eventually: ⇒ ρ 0, sample quasi-neutral again How long does it take for quasi-neutrality to be restablished? Answer: Dielectric relaxation time [see AT5.1 in notes]: τ d = σ Hence, for t τ d : ∂J t 0 ∂x Cite as: Jesús del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 11-4 Dielectric relaxation time τ d = σ Depends on doping level: The higher the doping level, the faster quasi-neutrality is established after a perturbation....
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lecture11 - 6.720J/3.43J Integrated Microelectronic Devices...

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