04 A Primer on the PN Junction

# 04 A Primer on the PN Junction - EE 474 A Primer on the pN...

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2/24/11 A Primer on the pN Junction EE 474

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2/24/11 A p-n junction is formed when these two materials are joined into a common device. The shape of the energy bands vs position play a major role in the electrical properties of the resulting device. Our goal is to understand the processes that lead to the shaping of the energy bands vs position and its analytical form. Forming a junction between two materials
2/24/11 5-3 Energy band diagram for the p n junction at equilibrium. This is the resulting shape of the energy bands vs position when the sample is in equilibrium. Note the Fermi energy does not depend on position, as expected. The conduction band

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2/24/11 Why are Ec and Ev functions of When n-type material is contacted to p-type material there are large gradients in the electron and hole concentrations because the density of electrons on the n side is large while the density of holes on the p side is large. Thus electrons in the vicinity of the junction will diffuse from the n side to the p side and holes in the vicinity of the junction will diffuse from the p side to the n side. These carriers become minority carriers when they cross the junction between the two materials and recombine within a minority carrier diffusion length, on average, on the other side of the junction. The n and p sides of the junctions were originally electrically neutral before the carriers diffused across the junction. Their loss from each side of the junction creates a charge imbalance with the n-side charged positively and the p side dx - E
2/24/11 The Solution to the Electrostatics Problem The variation of the energy bands as a function of position can be determined by solving for the electric field and the electrostatic potential that is

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## This note was uploaded on 02/23/2011 for the course EE 474 taught by Professor Lingo during the Spring '11 term at USC.

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04 A Primer on the PN Junction - EE 474 A Primer on the pN...

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