Abstract
Esaki and Tsu’s superlattice1, made by alternating two different semiconductor materials, was the first one-dimensional artificial crystal that demonstrated the ability to tailor semiconductor properties. One motivation of this work was the realization of the Bloch oscillator2,3 and the use of its particular dispersive optical gain4,5 to achieve a tuneable source of electromagnetic radiation. However, these superlattices were electrically unstable in the steady state6. Fortunately, because it is based on scattering-assisted transitions, this particular gain does not arise only in superlattices, but also more generally in semiconductor heterostructures7,8 such as quantum cascade lasers9 (QCLs), where the electrical stability can be controlled10. Here, we show the unambiguous spectral signature of Bloch gain in a special QCL designed to enhance the latter by exhibiting laser action in the condition of weak to vanishing population inversion.
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References
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Acknowledgements
This work was supported by the Swiss National Science Foundation and the National Center of Competence in Research, Quantum Photonics.
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The structures were designed by J.F. and grown by M.G. and N.H. using molecular beam epitaxy. T.G. fabricated the samples, worked on the measurement technique and measured the samples together with N.S. The theoretical work and the gain calculations were done by R.T. who also wrote the manuscript together with J.F., the head of the group in which the work was carried out.
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Terazzi, R., Gresch, T., Giovannini, M. et al. Bloch gain in quantum cascade lasers. Nature Phys 3, 329–333 (2007). https://doi.org/10.1038/nphys577
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DOI: https://doi.org/10.1038/nphys577
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