Quantum-cascade lasers in the 7-8 mu m spectral range with full top metallization

The paper demonstrates the generation of multistage quantum-cascade lasers (QCL) in the 7-8 mu m spectral range in the pulse generation mode. The active region structure we used is based on a two-phonon resonance scheme. The QCL heterostructure based on a heteropair of In0.53Ga0.47As/Al0.48In0.52As solid alloys was grown by molecular beam epitaxy and includes 50 identical stages. A waveguide geometry with top cladding with full top metallization (surface-plasmon quantum-cascade lasers) has been used. The developed QCLs have demonstrated multimodal generation in the 7-8 mu m spectral range in the pulse mode in the 78-250 K temperature range. The threshold current density for a 1.6 mm long laser and a 20 mu m ridge width amounted to similar to 2.8 kA/cm(2) at a temperature of 78 kappa. A temperature increase to 250 K causes a long-wave shift of the wavelength from 7.6 to 7.9 mu m and a j(th) increase to 5.0 kA/cm(2).