SiGe THz Quantum Cascade Lasers (QCLs)

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The terahertz (THz or 1012 Hz) is the part of the electromagnetic spectrum where most molecules have rotational and vibrational absorption modes and therefore is a rich area for molecular spectroscopy. The frequency range is also termed the far-infrared but the terahertz term was originally used for the region between photonic devices and electronic transit-time devices where few practical sources of radiation were previously available, termed the THz gap (roughly 200 GHz to 10 THz - or 30 µm to 1.5 mm wavelength). In the last 10 years this situation has changed significantly and there are many THz sources available with differing power, bandwidth and operating temperatures (see below). The frequency range is particularly interesting for medical and security imaging and spectroscopy as the radiation is non-ionising and hence is far safer than X-ray or gamma camera techniques.

We are working on producing a quantum cascade laser using Ge and SiGe epilayers grown on top of silicon substrates. As QCLs are unipolar, gain can be produced even in indirect bandgap material, unlike any interband laser.

We are a partner in the EC project Far-infrared Laser using Assembled Silicon Heterostructures (FLASH) led by Roma Tre with ETH Zurich, IHP and Nextnano.


  1. "Terahertz absorption-saturation and emission from electron-doped germanium quantum wells" Optics Express 28(5), pp. 7245 - 7258 (2020) - DOI: https://doi.org/10.1364/OE.381471
    C. Ciano, M. Virgilio, L. Bagolini, L. Baldassarre, A. Pashkin, M. Helm, M. Montanari, L. Persichetti, L. Di Gaspare, G. Capellini, D.J. Paul, G. Scalari, J. Faist, M. De Seta, and M. Ortolani

  2. "Design and simulation of losses in Ge/SiGe terahertz quantum cascade laser waveguides" Optics Express 28(4) pp. 4786 - 4800 (2020) - DOI: https://doi.org/10.1364/OE.384993
    K. Gallacher, M. Ortolani, K. Rew, C. Ciano, L. Baldassarre, M. Virgilio, G. Scalari, J. Faist, L. Di Gaspare, M. De Seta, G. Capellini, T. Grange, S. Birner, and D.J. Paul
    Terahertz complex refractive index data of silicon, germanium and silicon germanium

  3. "Room temperature operation of n-type Ge/SiGe terahertz quantum cascade lasers predicted by non-equilibrium Green's functions" Applied Physics Letters 114, 111102 (2019) - DOI: 10.1063/1.5082172
    T. Grange, D. Stark, G. Scalari, J. Faist, L. Persichetti, L. Di Gaspare, M. De Seta, M. Ortolani, D.J. Paul, G. Capellini, S. Birner, and M. Virgilio

  4. "Si/SiGe quantum cascade superlattice designs for terahertz emission" Journal of Applied Physics 107, 053109 (2010) - doi:10.1063/1.3319653 Article pdf
    G. Matmon, D.J. Paul, L. Lever, Z. Ikonic, M. Califano, R.W. Kelsall, D. Chrastina, G. Isella, H. von Känel, E. Müller and A. Neels

  5. "The progress towards terahertz quantum cascade lasers on silicon substrates" Laser and Photonics Reviews 4(5), 610 (2010) - doi:10.1002/lpor.200910038
    D.J. Paul

  6. "Interwell relaxation times in p-Si/SiGe asymmetric quantum well structures: the role of interface roughness" Physical Review B 75, 045338 (2007) - doi: 10.1103/PhysRevB.75.045338
    M. Califano, N.Q.Vinh, P.J. Phillips, Z. Ikonic, R.W. Kelsall, P. Harrison, C.R. Pidgeon, B.N. Murdin, D.J. Paul, P. Townsend, J. Zhang, I.M. Ross and A.G. Cullis

  7. "Low-loss surface-mode waveguides for terahertz Si/SiGe quantum cascade lasers" IEEE Journal of Quantum Electronics 42(12), pp1233-1238 (2006) - doi:10.1109/JQE.2006.883496
    A. De Rossi, M. Carras and D.J. Paul

  8. "Towards silicon-based lasers for terahertz sources" IEEE Journal of Selected Topics in Quantum Electronics 12(6), pp1570-1578 (2006) - doi:10.1109/JSTQE.2006.884069
    S.A. Lynch, D.J. Paul, P. Townsend, G. Matmon, Z. Suet, R.W. Kelsall, Z. Ikonic, P. Harrison, J. Zhang, D.J. Norris, A.G. Cullis, C.R. Pidgeon, P. Murzyn, B.N. Murdin, M. Bain, H.S. Gamble, M. Zhao and W.-X. Ni

  9. "Interwell intersubband electroluminescence from Si/SiGe quantum cascade emitters" Appl. Phys. Lett. 83(20), pp. 4092 - 4094 (2003) DOI: 10.1063/1.1626003
    R. Bates, S. A. Lynch, D. J. Paul, Z. Ikonic, R. W. Kelsall, P. Harrison, S. L. Liew, D. J. Norris, A. G. Cullis, W. R. Tribe and D. D. Arnone

  10. “Intersubband electroluminescence from Si/SiGe cascade emitters at terahertz frequencies” Applied Physics Letters 81, pp1543-1545 (2002) - doi:10.1063/1.1501759
    S.A. Lynch, R. Bates, D.J. Paul, D.J. Norris, A.G. Cullis, Z.Ikonic, R.W. Kelsall, P. Harrison, D.D. Arnone and C.R. Pidgeon

  11. “Picosecond intersubband dynamics in p-Si/SiGe quantum well emitters” Applied Physics Letters 80, pp 1456-1458 (2002) - doi:10.1063/1.1452794
    C.R. Pidgeon, P. Murzyn, J-P.R. Wells, I.V. Bradley, Z. Ikonic, R.W. Kelsall, P. Harrison, S.A. Lynch, D.J. Paul, D.D. Arnone, D.J. Robbins, D.J. Norris and A.G. Cullis