Indium antimonide detector for spectral characterization of terahertz sources

The goal of this study was to establish conditions under which a magnetic-field-tunable InSb detector can be used to characterize the radiation spectrum of terahertz (THz) sources. The response of a bulk InSb detector to a monochromatic radiation with the frequency 0.1 < f < 4.6 THz was studied at liquid helium temperatures and magnetic fields B up to 5 T. A constant voltage (measurements of photocurrent) or a constant current (measurements of photoresistance) biasing condition was tested, and both signals were found to be strongly influenced by magnetoresistance of the detector. At $f≲0.5$ THz, a photoresponse was observed in the whole range of B, which reflected a non-resonant absorption by free electrons and had no relation to cyclotron-resonance-related transitions. Resonant transitions developed gradually at $f≳0.5$ THz and dominated the spectra only at $f≳1.0$ THz. Thus, we show that only at this latter frequency range, the detector can be used for a spectral characterization of unknown sources. To avoid false interpretation of measured signals, a detector should be supplied with a 1-THz high-pass filter.