Predictable Quantum Efficient Detector

This thesis gives an overview of the Predictable Quantum Efficient Detector designed to measure optical radiation with theoretical relative uncertainty of 1 ppm (parts per million). The device is based on two custom made large area induced junction silicon photodiodes arranged in a wedged trap structure. High internal quantum efficiency (IQE) of the photodiodes is achieved by means of low doping concentration and usage of the reverse bias voltage. The IQE is predicted to be improved furthermore using low operating temperature close to 77 K. The losses due to reflected light are minimized by multiple reflections between the photodiodes. Low losses allow the PQED to work as an ideal quantum detector whose spectral responsivity is determined purely by the fundamental constants h, c, e and vacuum wavelength lambda. The remaining minor charge carrier losses are predictable using physical modelling whereas fractional reflectance losses can be measured. These properties classify the PQED as an absolute detector which does not require calibration against any other radiometric primary standard. The prototype PQED was compared against present primary standard - the cryogenic radiometer – at the wavelengths of 476 nm, 532 nm and 760 nm at room temperature and at liquid nitrogen temperature. Comparisons showed that the predicted external quantum deficiency of the PQED agreed with the measured external quantum deficiency within the expanded uncertainty of 60 ppm to 180 ppm determined by the cryogenic radiometer at both temperatures. These results indicate that the responsivity of the PQED is highly predictable and its uncertainty is comparable with the uncertainty of the conventional cryogenic radiometer. Such data provide evidence that the cryogenic radiometer operated close to 10 K temperatures may be replaced by a PQED operated even at room temperature. The advantage of the PQED is its simple operation which is comparable with any other silicon based photodetector whereas its optical radiation detection uncertainty is comparable with expensive and sophisticated cryogenic radiometer

Use of the Predictable Quantum Efficient Detector with Light Sources of Uncontrolled State of Polarization

Analysis of the reflectance losses of the Predictable Quantum Efficient Detector (PQED) operated at room temperature is presented. An efficient method of using the ratio of photocurrents from the two photodiodes of the PQED is developed to determine the reflectance losses without direct measurement of the reflectance for an unknown state of polarization of the incident light. A detailed analysis is presented to estimate the associated reflectance losses for detectors with either seven or nine internal reflections. For the seven-reflection PQED, the relative standard uncertainty component of spectral responsivity due to reflectance loss correction can be reduced typically below 100 ppm with the photocurrent ratio measurement whereas for the nine‑reflection PQED the uncertainties remain below 20 ppm in the wavelength range from 400 nm to 900 nm with an uncontrolled polarization state of the incident light

Predictable quantum efficient detector based on n-type silicon photodiodes

Timo Dönsberg et al. -- 16 pags., 16 figs., 4 tabs. -- Open Access funded by Creative Commons Atribution Licence 3.0The predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al2O3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488¿nm and 532¿nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatially uniform within 30¿ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of PQEDs is no longer dependent on the availability of a certain type of very lightly doped p-type silicon wafers.The research leading to these results has received funding from the European Metrology Research Programme (EMRP) project SIB57 'New Primary Standards and Traceability for Radiometry'. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. Financial support from the Academy of Finland through the Finnish Centre of Excellence in Atomic Layer Deposition is also acknowledged.Peer Reviewe

Wavelength calibration of Brewer spectrophotometer using a tunable pulsed laser and implications to the Brewer ozone retrieval

In this contribution we present the wavelength calibration of the travelling reference Brewer spectrometer of the Regional Brewer Calibration Center for Europe (RBCCE) at PTB in Braunschweig, Germany. The wavelength calibration is needed for the calculation of the ozone absorption coefficients used by the Brewer ozone algorithm. In order to validate the standard procedure for determining Brewer’s wavelength scale, a calibration has been performed by using a tunable laser source at PTB in the framework of the EMRP project ENV59 ATMOZ “Traceability for the total column ozone”. Here we compare these results to those of the standard procedure for the wavelength calibration of the Brewer instrument. Such a comparison allows validating the standard methodology used for measuring the ozone absorption coefficient with respect to several assumptions. The results of the laser-based calibrations reproduces those obtained by the standard operational methodology and shows that there is an underestimation of 0.8 % of the ozone absorption coefficients due to the use of the parametrized slit functions.This work has been supported by the European Metrology Research Programme (EMRP) within the joint research project ENV59 “Traceability for atmospheric total column ozone” (ATMOZ). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union

Sensitivity study of the instrumental temperature corrections on Brewer total ozone column measurements

The instrumental temperature corrections to be applied to the ozone measurements by the Brewer spectrophotometers are derived from the irradiance measurements of internal halogen lamps in the instruments. These characterizations of the Brewer spectrophotometers can be carried out within a thermal chamber, varying the temperature from -5 to +45ºC, or during field measurements, making use of the natural change in ambient temperature. However, the internal light source used to determine the thermal sensitivity of the instrument could be affected in both methods by the temperature variations as well, which may affect the determination of the temperature coefficients. In order to validate the standard procedures for determining Brewer’s temperature coefficients, two independent experiments using both external light sources and the internal halogen lamps have been performed within the ATMOZ Project. The results clearly show that the traditional methodology based on the internal halogen lamps is not sensitive to the temperature-caused changes in the spectrum of the internal light source. The three methodologies yielded equivalents results, with differences in total ozone column below 0.08% for a mean diurnal temperature variation of 10ºC.This work has been supported by the European Metrology Research Programme (EMRP) within the joint research project ENV59 “Traceability for atmospheric total column ozone” (ATMOZ)

Dual-mode room temperature self-calibrating photodiodes approaching cryogenic radiometer uncertainty

The room temperature dual-mode self-calibrating detector combines low-loss photodiodes with electrical substitution radiometry for determination of optical power. By using thermal detection as a built-in reference in the detector, the internal losses of the photodiode can be determined directly, without the need of an external reference. Computer simulations were used to develop a thermal design that minimises the electro-optical non-equivalence in electrical substitution. Based on this thermal design, we produced detector modules that we mounted in a trap structure for minimised reflection loss. The thermal simulations predicted a change in response of around 280 parts per million per millimeter when changing the position of the beam along the centre line of the photodiode, and we were able to reproduce this change experimentally. We report on dual-mode internal loss estimation measurements with radiation of 488 nm at power levels of 500 μW, 875 μW and 1250 μW, using two different methods of electrical substitution. In addition, we present three different calculation algorithms for determining the optical power in thermal mode, all three showing consistent results. We present room temperature optical power measurements at an uncertainty level approaching that of the cryogenic radiometer with 400 ppm (k = 2), where the type A standard uncertainty in the thermal measurement only contributed with 26 ppm at 1250 μW in a 6 hour long measurement sequenc

Temperature characterisation of Brewer determined in the laboratory

Presentación realizada en: ATMOZ Final Workshop, celebrado en Huelva el 2 de junio de 2017

Characterization of Dobsons instruments within EMRP ATMOZ Project

Presentación realizada en: ATMOZ workshop at 11th RBCC-E, celebrado en El Arenosillo, Huelva, el 1 de junio de 2017

Temperature characterisation of Brewer determined in the laboratory

Comunicación presentada en: Brewer Ozone Spectrophotometer/Metrology Open Workshop celebrado del 17 al 20 de mayo de 2016 en Ponta Delgada, Azores, Portugal.This work has been supported by the European Metrology Research Programme (EMRP) within the joint research project ENV59 "Traceability for atmospheric total column ozone" (ATMOZ