Thin Film Reflectance Model for Trap Detector

The physical model of the spectral responsivity of trap detector consists of multiple parameters such as the internal quantum efficiency and the spectral reflectance. In some measurement models, the spectral reflectance of the trap detector is approximated by fitting a wavelength dependence equation which does not consider the effect of the oxide thickness of the silicon photodiode. To analyse the uncertainty due to the oxide thickness variation, a thin film reflectance model is set up in the Standards and Calibration Laboratory (SCL) for the evaluation of the spectral reflectance of the trap detectors. The model is based on the Fresnel coefficients of a 3-layer thin film structure which consists of air and a thin film oxide layer on a silicon substrate. The reflectance model was implemented as user-defined functions to calculate the spectral reflectance at different oxide thickness. It was also integrated with the SCL’s MCM program to evaluate the uncertainty of the spectral responsivity of trap detectors.

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Measurement-based extrapolation of spectral responsivity by using a low-NEP pyroelectric detector

Measurement Science and Technology ◽

10.1088/1361-6501/ac3626 ◽

2021 ◽

Author(s):

Seongchong Park ◽

Dong-Hoon Lee ◽

Kee Suk Hong

Keyword(s):

Spectral Response ◽

Previous Method ◽

Pyroelectric Detector ◽

Spectral Responsivity ◽

Current Output ◽

Experimental Procedure ◽

Trap Detector ◽

Minimum Uncertainty ◽

Lock In ◽

Dc Current

Abstract In case the primary realization of the spectral responsivity scale is not conducted at all target wavelengths but at only a small part of them, one needs to extrapolate values at the specific wavelengths to an extended range. In this work, we present a fully experimental procedure to extrapolate a single value of spectral responsivity at 633 nm into the whole working wavelength range (250 – 1100) nm of Si photodiodes. It is based on spectral responsivity comparison between a Si trap detector and a low-NEP pyroelectric detector of nearly flat spectral response. For this purpose, we developed a setup specialized to compare a Si-trap detector of dc-current output with a pyroelectric detector of ac-voltage output by using a modulated probing light source and a monitoring technique. To keep the probing light chopped even for the dc-photocurrent readout, we adopted a low chopping frequency of 4 Hz and a triggered readout for the Si-trap detector, which leads to a speedy comparison between the Si-trap detector and the pyroelectric detector. For the reference pyroelectric detector, we characterized the spectral absorptivity of the black-coating and the nonlinearity of the lock-in amplifier readout. Compiling all the required information, the spectral responsivity of the Si trap detector could be measured with the minimum uncertainty of 0.3 % (k = 2), which was validated by comparing with that of our previous method based on a numerical extrapolation.

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