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What's the main differences between QCLs and ICLs in regard to laser characteristics?

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  • $\begingroup$ For example lower thresold current density for ICL compared to QCL, but I really don't know much about the resaon why it's like that. It may be somhow connected with the fact that the operating principle in ICLs is based on interband transitions rather than intersubband ->like in QCLs. $\endgroup$ Jun 10, 2017 at 15:52

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The threshold current density is indeed lower in ICLs than in QCLs, mostly because of the large difference in carrier lifetimes (~ nanosecond in the ICL, ~ picosecond in the QCL). The lifetime is intrinsically short for the intersubband lasers because of the fast intersubband scattering (from phonons or interface roughness).

There are many other differences. Here are some of them: (1) the QCLs are much less temperature sensitive; (2) the QCLs use more stages and can generate higher output powers from a single ridge; (3) the QCLs are unsuitable for vertical cavities because of low gain for in-plane-polarized light, whereas IC VCSELs have been recently demonstrated etc.

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QCLs are intersubband and do not depend on the bandgap. ICLs are cascaded but the lasing transition is from conduction to valence subband so they operate typically in the Near Infrared.

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The active regions of ICLs are typically type-II quantum wells, in which their bandgaps are determined mainly by the quantum well layer thickness rather than the bandgaps of the constituent materials. Hence, the bandgap of an ICL can be tailored to cover the entire mid-infrared spectrum.

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