We report on detailed carrier transport and optical properties in doped/undoped GaAs far-infrared (FIR)/terahertz (THz) mirror structures for GaAs-based FIR/THz device application. By the aid of variable magnetic field Hall and Shubnikov de Haas measurements, we have analyzed the carrier concentration, mobility and scattering times. It is found that ionized impurity scattering is the dominant scattering mechanism in the GaAs FIR/THz mirror structures. We investigate numerically the energy flux along the mirror depth and the reflection of the mirror structure. The experimental FIR/THz reflection and transmission spectra demonstrate the reliability of the optical analysis. (c) 2006 Elsevier B.V. All rights reserved.