Reduction of the threshold current density of GaAs/AlGaAs quantum cascade lasers by optimized injector doping and growth conditions

Since the first realization of quantum cascade lasers (QCL) in the GaAs material system in 1998, large progress has been made in the device performance of GaAs-based QCLs. However, the relatively high threshold current density of GaAs-based QCLs compared to InP-based QCLs is still the main obstacle for achieving high-temperature continuous wave operation in the GaAs material system. In this work, we investigate the GaAs/Al0.45Ga0.55As QCL-design published by Page et al. [Appl. Phys. Lett. 78 (2001) 3529] with 48 active periods embedded in a plasmon enhanced waveguide structure. The optimization of the growth conditions resulted in high-quality quantum cascade structures with operation temperatures up to room temperature. Essential for the fabrication of the high-quality layers was the use of different arsenic fluxes for the waveguide and the active region layers. Furthermore, we varied the doping level in the injector region and we found a strong dependence of this parameter on the threshold current density. The threshold current density is significantly reduced by a factor of 2 due to a decrease of the sheet carrier density by a factor of only 1.6. © 2005 Elsevier B.V. All rights reserved.