If a conducting electron reduces to the valence band in an LED, where does it get the energy to go back to the conductance band upon leaving the diode so current can flow? I'm confused as to how current can flow completely through an LED if all electrons are reduced to the valence electron state, meaning they are not conducting electricity. Do the electrons return back to the conductance band energy state?
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$\begingroup$ have a look at hyperphysics.phy-astr.gsu.edu/hbase/electric/miccur.html and hyperphysics.phy-astr.gsu.edu/hbase/Solids/band.html . $\endgroup$– anna vCommented Jun 3, 2019 at 11:39
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$\begingroup$ Note that an electron does not flow through an LED. Electrons from the n-type side encounter holes from the p-type side in the depletion layer. There they recombine (emitting light in the process in an LED). $\endgroup$– Jon CusterCommented Jun 3, 2019 at 13:10
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Dirac’s generalised ‘theory of holes’ in a stack of electron energy levels as corresponding to positive quasi- particles now forms the basis of our understanding of the quantum theory of solid state semiconductors and layered semiconductors known as ‘transistors’ [1]. The purity of the crystalline lattice structure of silicon gives rise to the valence and conduction energy levels in a semiconductor. An ‘n-p’ junction between a silicon wafer doped with excess electrons (n-type) and a wafer with few electrons (p-type) – equivalently with an excess of positively charged ‘holes�� - forms a diode since electrons can only flow one way; from the excess n-side to the deficit p-side; under an applied voltage. Creating light as it flows turns our diode into a Light Emitting Diode or LED. Adding another n-layer turns this diode into an n-p-n two state transistor ‘sandwich’.
[1] W Shockley (1951) ‘Electrons and Holes in Semiconductors with Applications to Transistor Electronics’, Bell Labs/van Nostrand.
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$\begingroup$ Okay. What impact does the activation voltage have on the semiconductor? How does the band gap link to this theory how do electrons decrease to the valence electron state but then increase back to conductance band state in order to exit the diode? $\endgroup$– EloiseCommented Jun 3, 2019 at 10:55
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1$\begingroup$ @Eloise if you have new questions you should post them as new questions. But also, you shouldn't expect a whole course in solid state physics to be presented by Q&A. You should take a course at your nearest college or self-study from a good book. $\endgroup$ Commented Jun 3, 2019 at 14:45