lecture20

lecture20 - 6.720J/3.43J - Integrated Microelectronic...

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Unformatted text preview: 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 20-1 Lecture 20 - The Si surface and the Metal-Oxide-Semiconductor Structure March 22, 2007 Contents: 1. The semiconductor surface 2. Ideal MOS structure at zero bias Reading assignment: del Alamo, Ch. 8, 8.1-8.2 (8.2.1-8.2.2) 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 20-2 Key questions How does the surface of a semiconductor look like at the atomic level? If one assembles a metal-oxide-semiconductor structure and sets it up at zero bias, what is the final situation? How does this picture change for different choices of metal work function? 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 20-3 1. Semiconductor Surface At a surface, perfect crystalline periodicity of solid comes to an abrupt end. What happens? Ideal semiconductor surface Semiconductor comes to an end, but bulk properties unaffected bonding arrangement at surface unchanged from bulk. E o virtual crystal semiconductor crystal E c E v ideal surface Zero carrier current normal to surface; other than that, carriers un- affected by surface. 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]. Real 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 20-4 surface In ideal surface, four-fold coordination of atoms cannot be preserved broken bonds surface is very reactive. Surface can lower its energy by: surface contamination : absorption of O, C, and other for- eign atoms and molecules surface reconstruction : surface atoms bond among them- selves. surface % contamination * E c # E v surface reconstruction bulk surface region near surface region with deformed bonding 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 20-5 Example of surface reconstruction: 7x7 (111) Si surface: Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007....
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lecture20 - 6.720J/3.43J - Integrated Microelectronic...

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