Study and realization of a transfer detector based on porous silicon for radiometric measurements

A photodetector of high accuracy has been developed at the "Laboratoire de Metrologie des Rayonnements (L.M.R)-Tunisia" to serve as a transfer detector for optical power measurements in the visible spectral range, i.e. wavelength from 400 to 800nm. The originality of the work, comparing with other ones, consists of realizing a pn(+) junction with a n(+) porous silicon layer on the front face and a zinc oxide (ZnO) film as a transparent electrode above the porous layer. This detector's structure permits to the porous silicon layer to trap the incident optical radiation and to reduce the reflection coefficient fluctuations of the front face to a value of about 7%. The uncertainties relating to the spatial response uniformity of the detector and especially in the central area with 5 mm diameter are equal to 0.5-0.7% for vertical and horizontal directions, respectively. The realized photodetector can roughly reach 10mW of measured optical power. This value represents an earning of one decade comparing with commercial photodiodes that cannot measure optical power beyond 1 mW. The photodetector presents a linearity with a cumulated deviation of a few 10(-4) through more than 4 decades with an uncertainty of 1.5 x 10(-4) at 1 sigma level. The photodetector was also indirectly calibrated with the cryogenic radiometer of the "Institut National de Wtrologie (INM)-France" and provides a convenient standard with a relative standard uncertainty of a few 10(-3) at the 1 sigma level. This uncertainty is equivalent to commercial transfer detectors used in metrology laboratories. (c) 2007 Elsevier B.V. All rights reserved.