Lec2.3 - initially deposited near the surface and A is the...

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EE330 Lecture # 2- continued: Donor: A doped semiconductor with extra electrons. (n type) Acceptor: A doped semiconductor with extra holes (p type) Important phenomenon at the graded junciton (p-n) : Diffusion, Drift During diffusion the concentration of impurities at the surface plays the most important role. If the concentration of the impurity is kept constant at the surface: N 0 impurity/cm 3 , then the distribution of impurity is approximated by: N(x,t) = N 0 erfc [ Dt x 2 ] #/cm 3 F.Y.I only – not to be studied. D: Diffusion constant - function of temperature and dopant type (cm 2 /s) t: length of time the diffusion takes place. D increases exponentially with temperature. p-n junction is formed below the surface where N A = N D . Thus the concentration function becomes: N(x,t) = [ Dt A Q π ]. e -x 2 /4Dt #/cm 3 F.Y.I only – not to be studied. If the total number of impurities is a fixed number. Where Q is the total number of impurities
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Unformatted text preview: initially deposited near the surface and A is the area (cm 2 ). The difference between the two equations is apparent at x=0. Equation 1 yields N=N and equation 2 yields a time varying function. Important: The potential that is built across the diode is a function of the number of Acceptor and Donor atoms: For example: AC model and DC models - Low and High Frequency models Small signal model at low frequencies: Capacitance can be ignored. Model is simply a resistor. It is also known as Dynamic Resistance. g I I n V di dv r D T D D 1 = + = = Dynamic signal model depends on temperature. ___________________________________________________________________________ Website to check: http://ocw.mit.edu/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6-071Introduction-to-ElectronicsFall2002/625CCF81-D846-43AF-94DF-72EB66DE5CD0/0/f02lec16.pdf...
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This note was uploaded on 03/03/2010 for the course EE EE330 taught by Professor Maryam during the Spring '10 term at CSU Long Beach.

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Lec2.3 - initially deposited near the surface and A is the...

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