Recent Advances in 3-5 microns InGaAs/InAlAs/InP quantum cascade lasers

In this paper, we discuss the limiting factors for short-wavelength QCL designs and how the incorporation of strain into the material can help to overcome the electron confinement limitations of QCLs at shorter wavelengths. As QCL designs approach shorter wavelengths, several problems arise, including electron confinement, intervalley leakage, surface plasmon loss, high power density, and non-uniform gain in the waveguide, all of which reduce device performance or even prevent operation completely. Problems associated with electron confinement arise as the upper laser level is pushed closer to the continuum by the wider separation of energy levels required for short-wavelength emission. High lattice and/or electron temperature leads to escape of electrons into the continuum, which manifests as leakage current.