Predictable Quantum Efficient Detector

Abstract

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.