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Gallium doped Germanium (Ge:Ga) Photoconductive Detector

Photoconductors can provide a greater speed of response than a composite bolometer, at the expense of a narrower range of operating frequencies. They operate at higher frequencies (shorter wavelengths) than hot electron bolometers.

Gallium doping in Germanium gives a useful photoconductive response out to wavelengths longer than any other combination of elements. In unstressed configurations, the cut-off wavelength is approximately 120 um. The measured spectral responsivity of stressed and unstressed detectors is shown in the figure below. NB We no longer offer stressed GeGa, as our InSb detectors can be combined with an unstressed GeGa conductor to give a similar spectral and temporal performance.


The performance characteristics of the detector depend critically on the operating conditions. In low radiation background conditions such as satellite astronomy, detector NEP can exceed 1 fW Hz-1/2, though the speed of response will be limited, to 20 Hz (– 3dB.) In higher background laboratory applications the detector may operate at 50 kHz (-3dB), albeit with much reduced sensitivity.

QMC Instruments Ltd. offers this versatile detector for all conditions, either as a stand-alone detector or configured into complete calibrated detector systems giving optimum performance for a particular set of experimental circumstances. As with all our cryogenic detector systems, cooling can be provided either by a mechanical (pulse tube) cooler or by liquid helium. 

Technical Specifications


Notes on specification

  • Test measurements made on a 4.2 K unstressed detector in relatively high radiation background. The source was a blackbody at 800 K.  Filtering comprises black polyethylene at 77 K and a 120 cm-1 low-pass powder filter at 4.2 K.

  • f/3 condensing cone with 3.5mm diameter aperture

  • 1.2 THz signal bandwidth centred at 3THz

  • 300 nW background power

  • 0.5 nW signal power 

A 2 year guarantee is provided as standard on all QMC Instruments Ltd products.

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