Implementing a Thin-Film Reflectance Model for Trap Detectors at the SCL

Abstract

The physical model of the spectral responsivity of trap detectors consists of multiple parameters such as the internal quantum efficiency and the spectral reflectance. In some measurement models, the spectral reflectance of trap detectors is approximated by fitting a wavelength dependence equation which does not consider the effect of the oxide thickness of the silicon photodiode. To analyze 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 trap detectors. The model is based on the Fresnel coefficients of a three-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 thicknesses. It was also integrated with the SCL’s MCM program to evaluate the uncertainty of the spectral responsivity of trap detectors.