The terahertz region (1-10THz) of the electromagnetic spectrum offers ample opportunities in spectroscopy, free space communications, remote sensing and medical imaging. Yet, the use of THz waves in all these fields has been limited by the lack of appropriate, convenient sources. We here report on a semiconductor heterostructure injection laser that emits at THz frequencies (4.44THz, lambda similar to 67 mum) and has the potential for device-like implementation. It is based on the quantum cascade scheme employing interminiband transitions in the technologically mature AlGaAs/GaAs material system and features a novel kind of waveguide loosely based on the surface plasmon concept. The electron dynamics in the structure is analysed with the help of Monte-Carlo simulations including both carrier-carrier and carrier-phonon scattering. The lasers emit more than 2 mW of peak optical power and can be operated in pulsed mode up to 60 K with threshold current densities of few hundred A/cm(2). Continuous-wave operation is achieved at temperatures below 30K with output powers of 150 muW.
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