Terahertz semiconductor-heterostructure laser

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Abstract

Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1–10 THz; 1 THz = 1012 Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications—for example, chemical detection, astronomy and medical imaging1,2,3,4. Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources5,6,7,8,9. Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4 THz, and already shows high output powers of more than 2 mW with low threshold current densities of about a few hundred A cm-2 up to 50 K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems.

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Figure 1: Conduction band structure of the laser active core and computed population inversion and current density at several applied biases.
Figure 2: Waveguide design principle and radiation mode confinement.
Figure 3: Emission spectra from a 1.24-mm-long and 180-µm-wide laser device recorded at 8 K for different drive currents.
Figure 4: Light–current (LI) characteristics of a 180-µm-wide and 3.1-mm-long laser ridge.

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Acknowledgements

We thank S. Dhillon for discussions.This work was supported in part by the European Commission through the IST Framework V FET project WANTED. R.K. was supported by the C.N.R.; E.H.L. and A.G.D were supported by Toshiba Research Europe Ltd and The Royal Society, respectively.

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Correspondence to Rüdeger Köhler.

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