Long wavelength (15 and 23 μm) GaAs/AlGaAs quantum cascade lasers

Quantum cascade lasers based on GaAs/AlGaAs chirped superlattice active regions have been achieved at wavelengths of 15 and 23 μm. In pulsed mode they operate up to temperatures of 220 and 100 K, respectively. While the 15 μm-laser employs a standard waveguide with n+-doped cladding, the 23 μm-laser was made with a metallic surface plasmon waveguide. The threshold current densities at cryogenic temperatures of 2.2 kA/cm2 (15 μm) and 10.2 kA/cm2 (23 μm) reflect the differences in intersubband lifetimes and waveguide losses close to the reststrahlenband.