Reflectance calculations for a predictable quantum efficient detector

Calculations of reflectance required for designing a predictable quantum efficient detector (PQED) are presented. The PQED will be based on natural inversion layer photodiodes and it is expected to measure optical power with an uncertainty of 1 ppm. To achieve such a low level of uncertainty, the associated reflectance of the PQED must be of the same order of magnitude. The wavelength range from 450 nm to 900 nm and the oxide layer thickness from 10 nm to 500 nm were used in the calculations of specular reflectance. The results show that a simple two-photodiode design is suitable for the PQED if scattering from the surface of the photodiode is less than 1 ppm. For higher scattering up to 100 ppm, a more advanced detector structure may allow control of this uncertainty component at the level of 1 ppm.