High accuracy measurement of the absolute spectral responsivity of Ge and InGaAs trap detectors by direct calibration against an electrically calibrated cryogenic radiometer in the near-infrared

This paper presents measurements of the absolute spectral responsivity of Ge and InGaAs trap detectors carried out by direct comparison with an electrically calibrated cryogenic radiometer (ECCR) in the near-infrared spectral range. Two tunable laser diodes were used as radiation sources operating between 1260 nm and 1360 nm and between 1460 nm and 1620 nm. The measurements of the cavity absorption and the Brewster-angled window transmission of the ECCR in these wavelength ranges are presented. A detailed analysis of the total measurement uncertainty is performed. The relative standard uncertainty of the responsivity measurement achieved is less than 5 x 10(-4) for all wavelengths investigated. The measurements are also discussed in terms of external spectral quantum efficiency, which is up to 90% for the Ge trap and up to 93% for the InGaAs trap. The determined spectral responsivities are compared with the existing scale for spectral responsivity at the Physikalisch-Technische Bundesanstalt ( the German National Metrology Institute) based on a thermopile detector. The deviation between the scales is at most +/- 0.15% for the InGaAs trap detector and at most +/- 0.30% for the Ge trap detector. The agreement is therefore within the combined standard uncertainties.