(GaIn)(AsBi) layers were grown on a GaAs substrate. Their alloy composition, structural characteristics as well as the optical and electrical parameters were determined. It was found that by incorporating Bi and In into the lattice of GaAs, the energy bandgaps can be as narrow as 0.6 eV. These epitaxial layers of quaternary bismide alloys have shorter than a one picosecond carrier lifetime and a relatively large dark resistivity, demonstrating that this material is a good candidate for ultrafast optoelectronics applications. Thick quaternary bismide layers were used for the fabrication of photoconductive antenna type THz radiation detectors activated by femtosecond laser pulses. The performance of THz detectors manufactured from (GaIn)(AsBi) layers was comparable to that of previously reported Ga(AsBi) devices, but the range of optical wavelengths at which the detectors can be activated was considerably wider, covering the technologically important 1.55 μm wavelength range.