Lecture6_diffusion_R-G

Lecture6_diffusion_R-G - ECE 3040: Microelectronic Circuits...

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ECE 3040 - Dr. Ying Zhang Georgia Tech ECE 3040: Microelectronic Circuits Lecture 6 Reading: Pierret 3.1-3.3
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Determination of Fermi Level Intrinsic Material: + + = c v v c i N N kT E E E ln 2 2 + + = * * ln 4 3 2 n p v c i m m kT E E E
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Determination of Fermi Level Extrinsic Material: = >> >> = >> >> = = i A i f i A D A i D i f i D A D i i i f n N kT E E n N and N N for or n N kT E E n N and N N for or n p kT n n kT E E ln ln ln ln
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Carrier Concentration Temperature Dependence Below a certain temperature, there are no free carriers (“freeze out”) In the mid-range, carrier concentration = doping level (“extrinsic region”) Above a certain temperature, every sample is intrinsic (n i is increased)
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ECE 3040 - Dr. Ying Zhang Georgia Tech At low electric field values, J p = qp μ p E and J n = qn μ n E μ is the “mobility” of the semiconductor and measures the ease with which carriers can move through the crystal. [ μ ]=cm 2 /V-Second Recapture Drift Current Density J = J p | Drift + J n | Drift = q( μ n n+ μ p p)E σ = q( μ n n+ μ p p) and ρ =1/[q( μ n n + μ p p)] Conductivity and Resistivity σ ~= q μ n n for n-type with n>>p σ ~= q μ p p for p-type with p>>n
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ECE 3040 - Dr. Ying Zhang Georgia Tech ± Band Bending ± Diffusion ± Einstein Relationship ± Recombination-Generation Agenda
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ECE 3040 - Dr. Ying Zhang Georgia Tech Energy Band Bending under Application of an Electric Field Energy Band Diagrams represent the energy of an electron. When an electric field is applied, energies become dependent on their position in the semiconductor. If only energy E g is added, then all energy would go to generating the electron and hole pair. Æ No energy left for electron/hole motion. (I.e the electron only has potential energy, and no kinetic energy). If energy E>E
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Lecture6_diffusion_R-G - ECE 3040: Microelectronic Circuits...

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