Self-calibration of semiconductor photodiodes in the soft x-ray region

A self-calibration procedure is presented for semiconductor photodiodes to be used as detectors in the soft x-ray region. In this procedure the spectral responsivity is calculated according to a model from experimentally accessible parameters of the detector. The thicknesses of the dead layer and the space charge region as well as the diffusion length have been determined in monochromatic radiation by investigating the angular dependence of the photocurrent. The mean energy for electron-hole pair creation has been determined in calculable undispersed synchrotron radiation of the primary standard source BESSY. The obtained uncertainties of the spectral responsivity in the photon energy region between 150 and 2500 eV are ≤4.2% for newly developed Si n on p diodes and ≤6% for GaAsP/Au diodes. The calibrated photodiodes were used to determine the quantum efficiency of photoemissive gold diodes which is up to four orders of magnitude lower than that of semiconductor photodiodes.