lecture8

# lecture8 - D I Zener The Barrier Voltage is large enough to...

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Physical Operation of Diodes Band Theory of Solids Some material from: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/intrin.html

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Doped Semiconductors Diffusion and Drift Diffusion dx dp qD J p p - = dx dn qD J n n = ) / ( 2 cm A J ) 3 / ( cm atoms p and n s cm D s cm D s cm D n p / 35 ; / 12 ); / ( 2 2 2 = = D Diffusion constant or Diffusivity Drift E v E v n drift n p drift p μ = = - - ; E qn J E qp J n drift n p drift p = = - - ; E n p q J n p drift ) ( + = s V cm s V cm mobilty Vs cm n p 2 2 2 1350 ; 480 ; ) / ( pn Junction Under Open Circuit Conditions Majority carriers drift towards opposite region. There they recombine with opposite carriers and disappear. A depletion area is created and bound charge is uncovered. A voltage difference is created and a drift current on the minority carries is created to make net current 0
pn Junction Under Open Circuit Conditions 0 2 0 1 1 2 ; ln V N N q W n N N V V D A S dep i D A T + = = ε pn Junction Under Reverse-Bias Conditions I I I D S = - ) ( 1 1 2 0 R D A S dep V V N N q W + + = pn Junction Under Breakdown Conditions When I is large enough to make 0 = D I ( I I I D S = - ), as S I can not change, another mechanism produces

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Unformatted text preview: D I . Zener The Barrier Voltage is large enough to break the Fermi Level, more carriers, an D I generated Avalanche The kinetic energy of the electrons is enough tp break covalent bonds and generate D I pn Junction Under Forward-Bias Conditions pn Junction Under Open Forward-Bias Conditions Minority Carrier Distibutions T V V n n n e p x p / ) ( = [ ] p n L x x n n n n n e p x p p x p / ) ( ) ( ) (---+ = The Minority Carrier distributions will increase Id to the required level and the barrier voltage will be reduced by V dx dp qD J p p-= [ ] p n T L x x V V n p p p e e p L D q J / ) ( / 1---= At the Junction [ ] 1 /-= T V V n p p p e p L D q J Similarly: [ ] 1 /-= T V V p n n n e n L D q J [ ] 1 /- + = T V V n p n p n p e L n D q L p D q A I...
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lecture8 - D I Zener The Barrier Voltage is large enough to...

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