lec5 - 6.012 - Microelectronic Devices and Circuits - Fall...

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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 5-1 Lecture 5 - PN Junction and MOS Electrostatics (II) pn Junction in Thermal Equilibrium September 22, 2005 Contents : 1. Introduction to pn junction 2. Electrostatics of pn junction in thermal equilibrium 3. The depletion approximation 4. Contact potentials Reading assignment: Howe and Sodini, Ch. 3, §§ 3.3-3.4
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 5-2 Key questions What happens if the doping distribution in a semi- conductor abruptly changes from n-type to p-type? Is there a simple description of the electrostatics of a pn junction?
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 5-3 1. Introduction to pn junction pn junction: p-region and n-region in intimate contact Why is the p-n junction worth studying? It is present in virtually every semiconductor device! Example: CMOS cross section p n n p + n + n + p + p + n + PMOS NMOS Understanding p-n junction is essential to understanding transistor operation.
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 5-4 2. Electrostatics of p-n junction in equilibrium Focus on intrinsic region: p n metal contact to n side metal contact to p side ( N a ) ( N d ) x = 0 (b) n type p type p type x x (a) Doping distribution of abrupt p-n junction: N N d x 0 N a p-region n-region
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 5-5 What is the carrier concentration distribution in thermal equilibrium? First think of two sides separately: log p o , n o p o p o n o n o N d n i 2 N d x N a n i 2 N a minority carrier minority carrier majority carrier majority carrier p-region n-region Now bring them together. What happens?
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lec5 - 6.012 - Microelectronic Devices and Circuits - Fall...

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