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A 1.8-THz quantum cascade laser operating significantly above the temperature of ω/kB


Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to 1.9ω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser.

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Figure 1: Resonant-tunnelling versus scattering-assisted injection for terahertz quantum cascade lasers.
Figure 2: Reduction in the operating dynamic range with frequency for resonant-tunnelling injection.
Figure 3: A 1.8-THz QCL based on the scattering-assisted injection design scheme.
Figure 4: Experimental results as a function of temperature.

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This work is supported by the National Aeronautics and Space Administration and the National Science Foundation. The work was carried out in part at the United States Department of Energy, Center for Integrated Nanotechnologies, and Sandia National Laboratories (Contract DE-AC04-94AL85000).

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Authors and Affiliations



S.K. designed the quantum cascade structure in consultation with Q.H., processed the devices and did some initial experiments. C.W.I.C. carried out detailed experiments and characterization. S.K., C.W.I.C. and Q.H. analysed the experimental data. J.L.R. was responsible for the crystal growth by molecular beam epitaxy. S.K. wrote the manuscript with assistance from all other authors. The project was supervised by Q.H.

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Correspondence to Sushil Kumar.

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The authors declare no competing financial interests.

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Kumar, S., Chan, C., Hu, Q. et al. A 1.8-THz quantum cascade laser operating significantly above the temperature of ω/kB. Nature Phys 7, 166–171 (2011).

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