Jarle Gran

Predictable quantum efficient detector: II. Characterization and confirmed responsivity

The predictable quantum efficient detector (PQED) is intended to become a new primary standard for radiant power measurements in the wavelength range from 400 nm to 800 nm. Characterization results of custom-made single induced junction photodiodes as they are used in the PQED and of assembled PQEDs are presented. The single photodiodes were tested in terms of linearity and spatial uniformity of the spectral responsivity. The highly uniform photodiodes were proved to be linear over seven orders of magnitude, i.e. in the radiant power range from 100 pW to 400 µW. The assembled PQED has been compared with a cryogenic electrical substitution radiometer with a very low uncertainty of the order of 30 ppm. Experimental results show good agreement with the modelled response of the PQED to optical radiation and prove a near unity external quantum efficiency.

Simulations of a predictable quantum efficient detector with PC1D

The spectral responsivity of a predictable quantum efficient detector (PQED) is calculated based on the responsivity of an ideal quantum detector and taking into account reflection losses from the surface of the photodiode and internal charge-carrier gains/losses inside the diode. The internal quantum deficiency (IQD) is obtained from simulations with the PC1D software using the material data of the produced PQED photodiodes. The results indicate that at room temperature the predicted IQD of the PQED is close to zero with an uncertainty of about 100 ppm over the visible range. It is further concluded that a primary standard of visible optical power with an uncertainty of approximately 1 ppm is achievable using the PQED at low temperatures.

Absolute calibration of silicon photodiodes by purely relative measurements

Previously verified models of windowless silicon photodiodes can be used to estimate their spectral response by purely relative measurements. The spectral reflectance is found from a single measurement at one wavelength to estimate the oxide thickness, from which the full spectral reflectance is calculated. The internal quantum deficiency of the silicon detector is found by fitting a physical model to a purely relative measurement to a spectrally invariant detector. The detector model ensures correct scaling of the responsivity. This method contributes to simplification of the traceability and promises a very cost efficient realization of an accurate independent spectral response scale. We have measured the responsivity of a silicon trap detector with this method. An uncertainty less than 0.20% was observed with 95% confidence in the spectral range from 455 nm to 760 nm. The uncertainty was calculated from the observed variance in the relative spectral response measurement. The uncertainty was limited by the signal to noise ratio (SNR) in the measurements of the relative spectral response of the silicon trap detectors.