Talk:Quantum cascade laser

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To-do list for Quantum cascade laser:	edit · history · watch · refresh
Here are some tasks you can do: Requests: Create a section on the history of QCL development - from their proposal to recent landmark developments. It should not become a boring list of every QCL developed by every group in history! Verify: Add references to the Material system section. Expand: Expand the description of active region designs to compare the most commonly used designs: resonant phonon, bound-to-continuum, hybrid designs etc. Stubs: Complete sections for Emission wavelengths, optical waveguides, growth and applications.
Priority 5

Contents 1 Charge Carriers 2 Device Fabrication 3 Who is the inventor of QCL? 4 Diagrams 5 Major Typos 6 Optical Waveguides

[edit] Charge Carriers

The statement that electrons are the only charge carrier is ambiguous. Devices have been successfully demonstrated, which exploit intersubband transitions in the valence band. Of course, electron transport is taking place here, but one may refer to the process as hole transport when the majority of electron states in a band are occupied. I think the important point here is that intersubband transitions rather than interband transitions are taking place. - djsik 17:39, 11 March 2006 (UTC)

Reading over this, I should probably have said that electroluminescence has been observed for valence band transitions in SiGe. I'm not so sure about lasing. Anyway, the point stands that in principle, I'm not aware of a reason why hole transitions could not be exploited in a QCL. Anyone else more knowledgeable about this? Alex valavanis 00:04, 2 February 2007 (UTC)

Yeah, they've definitely found electroluminesence in IV/IV semiconductors-- no lasing, though. The band jumps simply aren't big enough in SiGe. —Preceding unsigned comment added by 67.85.179.182 (talk) 09:22, 30 January 2008 (UTC)

I'd argue that it's more to do with complexity of the valence bandstructure. At k=0, the heavy-hole band offset is quite large (~400meV I think) but as you move to non-zero in-plane wave-vectors, increasingly large contributions from the light-hole band are mixed in. This makes it very difficult to predict the scattering behaviour, reduces the effective band offset and increases the emission linewidth (which kills the gain!) There's still a chance though, that at very low temperatures it may be possible. There are also several groups looking at conduction subbands, but no decent experimental results yet. Papa November (talk) 09:42, 30 January 2008 (UTC)

[edit] Device Fabrication

Although MBE is commonly used, I believe CVD is too. Does anyone know more about this? - djsik 17:39, 11 March 2006 (UTC)

MBE was orginally used most often for the first decade because Alfred Cho, the inventor, was a member of the research group. MBE growth gives much cleaner layers. Interest in MO-CVD growth began relatively recently and has been growing due to the already-in-place industry growth facilities. This would make the industrial production of QCLs cheaper and more feasible.

Responding to this query: It has long been a goal to build QCLs by MOCVD because that makes production much cheaper. I believe a proof of principle has been achieved (I think by HP labs) but it was a very low quality device and it is not clear if this technology will really be made feasible. —Preceding unsigned comment added by 98.173.26.151 (talk) 14:54, 14 December 2007 (UTC)

[edit] Who is the inventor of QCL?

Orignal concept was published by Kazarinov and Suris in 1971 and then realized by the group at Bell Labs. I think the credit of invention should go to the original authors: "Possibility of amplification of electromagnetic waves in a semiconductor with a superlattice",Kazarinov, R.F.; Suris, R.A., Fizika i Tekhnika Poluprovodnikov April 1971, vol.5, no.4, pp. 797-800

[edit] Diagrams

There are some nice public domain images over on the Netherlands version of this page (nl:Kwantumcascadelaser); would anyone care to have a go at incorporating them here? — Catherine\^talk 08:06, 23 February 2007 (UTC)

[edit] Major Typos

The equation starting dn1/dt in the section "Operating Principles" is all wrong. It should read dn1/dt = n2/tau21 + n3/tau31 - n1/tau13 - n1tau12 - Iout

[edit] Optical Waveguides

All QCLs ever published make use of a waveguide. What is this section supposed to mean? —Preceding unsigned comment added by 192.167.204.12 (talk) 13:35, 28 November 2007 (UTC)

You're quite right! I've tidied it up. We need to improve this section a lot - there's plenty that can be said about QCL waveguides. Papa November (talk) 14:25, 28 November 2007 (UTC)