Response of silicon diodes for synchrotron radiation

Because of very high intensity and pulsed nature of synchrotron radiation the nonlinear effects in recombination-generation kinetics must be taken into account in the response of silicon diodes under irradiation. Dependences of the charge carrier lifetime and the ambipolar diffusion coefficient on the excess carrier density generated by the synchrotron radiation have been considered. Response of silicon diodes on photons from synchrotron sources with energy 20-100 keV has been calculated using the Shockley-Reed recombination statistics. Diffusion equation with time-dependent generation functions has been solved numerically for various intensity of the photon beam and parameters of diodes (diodes design and characteristics of impurity centers). Optimal choice of parameters of diodes for the short-cut current and the photovoltaic operation mode are discussed. Dependencies of responses on the generation rate can be converted into the dose rate responses of diodes by calculating the energy deposition in silicon. At very high beam intensity (the excess minority carrier density is much larger than the density of the majority charge carriers), the Shockley-Reed recombination model would be invalid and the Auger recombination becomes dominant. To explain experimental data on the dose rate response it is needed to use a correct function of the excess carrier lifetime versus the carrier density.