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Unformatted text preview: 6.720J/3.43J Integrated Microelectronic Devices Spring 2007 Lecture 71 Lecture 7 Carrier Drift and Diffusion (cont.) February 20, 2007 Contents: 1. Nonuniformly doped semiconductor in thermal equi librium Reading assignment: del Alamo, Ch. 4, 4.5 Cite as: Jess 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 72 Key questions Is it possible to have an electric field in a semiconductor in ther mal equilibrium? What would that imply for the electron and hole currents? Is there a relationship between mobility and diffusion coecient? Given a certain nonuniform doping distribution, how does one compute the equilibrium carrier concentrations? Under what conditions does the equilibrium majority carrier con centration follow the doping level in a nonuniformly doped semi conductor? Cite as: Jess 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 73 1. Nonuniformly doped semiconductor in thermal equilibrium It is possible to have an electric field in a semiconductor in thermal equilibrium nonuniform doping distribution Gauss Law: electrical charge produces an electric field: d E = dx volume charge density [ C/cm 3 ] if = 0 d E = 0 dx in a certain region, it is possible to have E = 0 with = 0 if there are charges outside the region of interest In semiconductors: = q ( p n + N D + N A ) If N D + N D and N A N A , d E q = ( p n + N D N A ) dx Cite as: Jess 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 74 d E q = ( p n + N D N A ) dx Uniformlydoped semiconductor in TE: far away from any surface charge neutrality : o = 0 d E o = 0 dx since no field applied from the outside E o = 0 Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007....
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This note was uploaded on 09/24/2010 for the course EECS 6.720J taught by Professor Jesúsdelalamo during the Spring '07 term at MIT.
 Spring '07
 JesúsdelAlamo

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