Note for ECE 432 at OSU
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This 2 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at Ohio State University taught by a professor in Fall. Since its upload, it has received 29 views.
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Date Created: 02/06/15
Notes on p n junctions ECE 432 Prof Siddharth Rajan Ohio State University These notes are valid for abrupt pn junctions Where both 11 and p regions are doped nondegener ately Important note kT is thermal energy it can be expressed in eV or in Joules How are eV and J related 1 eV is 16 X 103919 J 1 eV is the energy gained by an electron which has a charge of 16 X 103919C When it gains 1 V kT q is the thermal voltage and its unit is V In the equations given below ES is the permittivity of the semiconductor for details see note below and VA is the voltage applied on the pside of the junction For equilibrium set VA 0 V Builtin voltage This is the rst step in analyzing any pn junction n2 71 Units V Depletion widths Depletion Width on nside x 2 265Vbi VA NA 1 12 N 1 ND NAND Units cm Depletion Width on pside zeal VA ND 1 2 xP q ElNAND Units cm Total depletion Width x ltN ANDgtgt 2 N P 4 NA ND Units cm Electric eld The maximum electric eld occurs at the metallurgical junction The value of the maximum electIic eld is given by Note how this expression and the one for W are both symmetric as expected Why is this expected Units Vcm 2 pn junction electrostatics nb Depletion Capacitance The depletion capacitance of a pn junction is given by ES Cdep W Units F cm2 Note about Es permittivity of the semiconductor Semiconductors are dielectrics and therefore have a different effective permittivity from vac cum The permittivity of a semiconductor is given by es e 60 Where 6 is the relative dielectric constant of the semiconductor You can find it in your table it Will be of the order of 10 For example it is 119 for Silicon 16 for Germanium It has no units 60 is the permittivity of vacuum In cmunits it is 885 X 103914 Fcm Therefore ES has the same units as 60
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