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.