We studied far-infrared (FIR) response due to cyclotron resonance (CR) of two-dimensional electron gas systems in GaAs/AlGaAs heterostructures by using cyclotron radiation from n-InSb devices as the illumination source. We examined the dependence of the FIR response on different experimental parameters, including the aspect ratio of Hall bars, electron mobility, bias current, illumination intensity, magnetic field, and lattice temperature. A strong photoresponse emerges only in the vicinity of integer quantum Hall effect (IQHE) regimes. Time-resolved measurements show that the recombination lifetime of excited carriers depends largely on the electron mobility, ranging from 5 μs to 1 ms at 4.2 K. The temporal decay of photoresponse is nonexponential in higher-mobility samples, whereas it is exponential with a single time constant in lower-mobility samples. This, together with the relatively large time constants, suggests that the FIR response is induced through multitrapping processes, in which excited carriers in Landau levels are repeatedly captured by localized states and reexcited to delocalized states. This multitrapping process is suggested to be promoted by the CR-induced heating of the electron system. Theoretical calculation based on the electron heating model reasonably reproduces characteristic dependence of the photoresponse on the magnetic field in the vicinity of IQHE plateaus. The IQHE Hall bars serve as a high-sensitive narrow-band FIR detector, where the highest sensitivity reaches ∼108 V/W. Tunability of the detector is demonstrated by varying the electron density. We discuss briefly the design of high-sensitive FIR detectors using the IQHE Hall bars. © 2001 American Institute of Physics.