Quantum Well Optical Devices

/ edmundsj
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In this video, we start to explore new types of optical devices - ones made with quantum wells. These represent the vast majority of all modern optical devices, and it is likely most solid-state LASERs you encounter in practice use quantum wells. We explore the major differences between 'bulk' devices and quantum well devices, as well as what understanding we get to keep and what we have to modify.
This is part of my graduate series on optoelectronics / photonics, and is based primarily on Coldren's book on Lasers as well as graduate-level coursework I have taken in the EECS department at UC Berkeley.
Hope you found this video helpful, please post in the comments below anything I can do to improve future videos, or suggestions you have for future videos.

[@sagarsaini1991]

great video

[@Heroofutopia]

Thanks

[@cstephenmurray]

Not a comment, but a question. I am a high school physics teacher teaching an Advanced Physics class and am a bit out of my league. In Randall Knight's 1-D Quantum Mechanics Chapter (p1297) he talks about a GaAlAs-GaAs-GaAlAs quantum laser with a 1.0 nm GaAs layer. He says the U of the electron is 0.30eV less than the surrounding GaAlAs layers, giving a SINGLE quantum state, n=1 E = 0.125 eV. Quoting "Every electron trapped in this quantum well has the same energy - a very nonclassical result! The fact that the electron energies are so well defined, in contrast to the range of electron energies in bulk material, is what makes this a useful device. ...the probability density of the electrons are more likely to be found in the center of the layer than at the edges. This concentration of electrons makes it easier for the device to begin laser action." Previously we learned that laser action requires population inversion. How does this happen in the quantum laser if there is only one energy level? Thank you in advance for any help you can give.

[@JordanEdmundsEECS]

Excellent question - it doesn’t. There is a second energy level he doesn’t talk about that is assumed to be empty below the valence band that the electron can drop into. If this state is also full, there won’t be any lasing. Don’t worry, we’re all out of our depth ;). Especially me.

[@teijironishimura6570]

To understand the population inversion of semi-conductor lasers, you need to know that for every electron in the quantum state, n = 1 E = 0.125 eV, there is a hole (or a void left by that electron) in a similar quantum state. To understand why this hole exists, you need to know that in semi-conductors an electron will only be in a "quantum state" if they are excited up to that state (via thermal excitation and doping). When the electron is excited into this quantum state, it leaves behind a hole that is also at a single quantum state. The way a semi-conductor laser gives off light is through the recombination of the excited electron and hole. Because both the hole and electron are at a single quantum state, when they recombine (through stimulated emission) they will only give off one frequency, thus you get a laser. So to answer you question, population inversion in semi-conductor laser is really just this electron-hole pairing you get.

[@oakdeepvastforest2924]

Another guy who cannot focus on an idea and fills the presentation with rubbish words. Be exact mate. And drop the "ah", it's really not cool repeating it so many times.