This communication presents experimental study of the asymmetrically-shaped bulk GaAs and modulation-doped GaAs/Al0.25Ga0.75As structures as active parts of detectors of electromagnetic radiation in GHz-THz frequency range at room temperature. The devices employ non-uniform carrier heating induced by both the asymmetrical shape of the structure and the presence of the n-n(+)-junction, Frequency dependence of the voltage sensitivity is given and discussed in the range from 10 GHz up to 2.5 THz. The results at THz frequencies are compared with those of GaAs/AlAs-superlattice-based device.