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InSb hot electron bolometer


  • High sensitivity and low noise

  • Fast operating speeds of ~500 KHz

  • Tuneable peak frequency up to 2.5 THz

  • Can be arrayed

  • Cryogenically cooled

  • Available in wet or dry systems


Indium antimonide (InSb) bolometers offer much shorter time constants than composite germanium bolometers or Nb TES bolometers, at the expense of a narrower range of operating frequencies. Sensitivity at frequencies above 500 GHz can be improved with magnetically enhanced versions of this detector.

QMC Instruments Ltd. offers a high sensitivity InSb hot-electron bolometer that can be operated at 4.2 K. The detector is most commonly mounted in an optical integrating cavity behind Winston Cone coupling optics along with low-pass filters which ensure that unwanted higher frequencies are efficiently rejected.

An InSb (size 5 mm x 4.7 mm x 300 um) detector mounted on a quartz substrate is shown in the picture above. Detectors can be purchased as a stand-alone unit or as part of a fully assembled, tested and calibrated detector system ready for use.

We offer 3 different types:


Our QFI X is a meander of InSb that is highly sensitive to frequencies between 60 - 500 GHz, whilst providing fast response times.


The homogeneously tuned detector – model QFI/XB which uses a uniform magnetic field exposure, creating a single peaked response function. The peak frequency can be tuned between 1.5 and 2.5 THz and the typical peak width is 300 GHz at full-width-half-maximum.

Please see graph below for how our magnetically tuned detectors compare:


The inhomogeneously tuned detector – model QFI/XBI uses a varying magnetic field strength across the detector. The resonance is therefore integrated over a wider frequency range up to a maximum of 1.5 THz

Tuned InSb.jpg

Operating Principles

Indium Antimonide (InSb) is a III-V semiconductor used commonly as a detector in the near-infrared. At 4.2 K the electron-phonon interactions are very weak, compared to the electron-electron interactions. This means that the absorption of long wavelength radiation can drive the electrons out of thermal equilibrium with the lattice to a hotter temperature. Termed the hot-electron response, it was first predicted by E.H.Putley in 1960. Since the resistance of the InSb depends on the electron temperature, then the resistance can be used as a thermometer of the electron system, and therefore indirectly ​a monitor of the incident radiation.

Magnetic tuning

In InSb at 4.2 K the absorption will be constant up to 500 GHz, beyond which it falls as the signal frequency to the power -1.8. The result is that the unassisted detector (model QFI/X) loses a factor of almost 10 in sensitivity at 1.5 THz and more than a factor of 20 at 2.5 THz. However, by applying a magnetic field we can shift the absorption to higher frequencies.

Technical Specifications


Notes on specification

  • Detector optical responsivity is specified at 275 GHz

  • Detector optical NEP is specified at 275 GHz (1 kHz modulation)

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