Room-temperature operation of λ≈7.5 μm surface-plasmon quantum cascade lasers

We report the pulsed, room-temperature operation of λ≈7.5 μm quantum cascade lasers (QCLs) in which the optical mode is a surface-plasmon polariton excitation. Previously reported devices based on this concept operate at cryogenic temperatures only. The use of a silver-based electrical contact with reduced optical losses at the QCL emission wavelength allows a reduction of the laser threshold current by a factor of 2 relative to samples with a gold-based contact layer. As a consequence, the devices exhibit room-temperature operation with threshold current densities ∼6.3 kA/cm². These devices could be used as all-electrical surface-plasmon generators at midinfrared wavelengths.