Lecture7-DriftDiffusionChap3Pierret

# Lecture7-DriftDiffusionChap3Pierret - Lecture 7 Drift and...

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ECE 3040 - Dr. Alan Doolittle Georgia Tech Lecture 7 Drift and Diffusion Currents Reading: Pierret 3.1-3.2

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ECE 3040 - Dr. Alan Doolittle Georgia Tech Ways Carriers (electrons and holes) can change concentrations •Current Flow: •Drift: charged particle motion in response to an electric field. •Diffusion: Particles tend to spread out or redistribute from areas of high concentration to areas of lower concentration •Recombination: Local annihilation of electron-hole pairs •Generation: Local creation of electron-hole pairs
ECE 3040 - Dr. Alan Doolittle Georgia Tech Drift •Direction of motion: •Holes move in the direction of the electric field (from + to -) •Electrons move in the opposite direction of the electric field (from - to +) •Motion is highly non-directional on a local scale, but has a net direction on a macroscopic scale •Average net motion is described by the drift velocity, v d with units cm/second •Net motion of charged particles gives rise to a current Direction of net motion + - Instantaneous velocity is extremely fast

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ECE 3040 - Dr. Alan Doolittle Georgia Tech Drift Current Density J [A/cm 2 ] Electric Field [V/cm] - Electron Motion + Hole Motion Given current density J (I=J x Area) flowing in a semiconductor block with face area A under the influence of electric field E, the component of J due to drift of carriers is: J p | Drift = q p v d and J n | Drift = q n v d Area A Hole Drift current density Electron Drift current density
ECE 3040 - Dr. Alan Doolittle Georgia Tech

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