Quasi-Fermi Levels Lesson

by Greg Lush

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4 Lesson Topic: Quasi-Fermi Levels
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6 Objective of Lesson: To understand quasi-Fermi levels.
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8 Reading Assignment: Section 3.5.2
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10 What do you need to know for the exam?
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12   1. You should be able to place a quasi-Fermi level in the band diagram.
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14 Summary
15 The quasi-Fermi levels are used to specify (in equations and in the band diagram) the carrier concentrations under non-equilibrium conditions.
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17 Quasi-Fermi levels
18 The quasi-Fermi levels are used to specify (in equations and in the band diagram) the carrier concentrations under non-equilibrium conditions. The way I like to put it is to say that in equilibrium, one Fermi level is enough because pono = ni2. Out of equilibrium the carrier concentrations may have changed and if they have, typically pn ≠ pono. One of the results of this is that one Fermi level is no longer sufficient for describing or calculating the carrier concentrations.
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20 The section in the text is excellent on this subject so there is not much more that I need to lay out for you.
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22 -
In the band diagram the location of the quasi-Fermi levels provides visually an estimate as to whether the semiconductor is in low-level injection, and what the level of injection is in a "quasi-"quantitative way :).<br><br>
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In the band diagram, the location of the quasi-Fermi levels provides visually an estimate as to whether the semiconductor is in low-level injection, and what the level of injection is in a "quasi-"quantitative way :).<br><br>
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24 We will not use quasi-Fermi levels a lot, but they are important and useful concepts at times so you need to be aware of them and the equations in which they find themselves (see text section).
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26 Definitions
27   Quasi: A prefix meaning, to some degree or in some manner.
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