Quantum cascade lasers with double metal-semiconductor waveguide resonators

Quantum cascade (QC) lasers with double metal-semiconductor waveguide resonators are reported for operating wavelengths of 19, 21, and 24 μm. The waveguides are based on surface-plasmon modes confined at the metal-semiconductor interfaces on both sides of the active region/injector stack and are not restricted by a cutoff wavelength for the TM polarized intersubband radiation. The double metal-semiconductor resonator devices are fabricated using an epilayer transfer process. Optical confinement factors close to 1 are obtained, with low waveguide losses. The performance of the devices is compared with that of QC lasers based on single-sided surface-plasmon waveguides. The concept of QC laser with double metal-semiconductor waveguide is applicable to a much wider wavelength range.