GaAs Quantum Cascade Lasers: Fundamentals and Performance

Abstract
Quantum engineering of the electronic energy levels and tailoring of the wavefunctions in GaAs/AlxGa1−xAs heterostructures allows to obtain the correct matrix elements and scattering rates which enable laser action between subbands. This article reviews the state-of-the-art of GaAs based quantum cascade lasers. These new light sources operate, with peak power in excess of 1 W at 77 K, in the 8–13 μm wavelength region, greatly extending the wavelength range of GaAs optoelectronic technology. Waveguides are based on an Al-free design with an appropriate doping profile which allows optical confinement, low losses and optimal heat dissipation. Finally, new active region designs aiming to improve the laser temperature dependence are discussed. Recent results on these devices confirm that the ratio between the conduction band discontinuity and the photon energy (ΔE_c/E_laser) is the dominant parameter controlling their thermal characteristic. The maximum operating temperature of these devices is 280 K for lasers with emission wavelength at ~11 μm.