X-ray absolute calibration of the time response of a silicon photodiode

The time-dependent response of a 1-mm2 silicon photodiode was characterized by use of pulsed synchrotron radiation in the 4- to 16-nm-wavelength range. Modeling the input radiation pulse and the electrical response of the photodiode allowed the photodiode's capacitance as a function of wavelength and applied bias voltage to be determined. The capacitance was in the 7- to 19-pF range and resulted in response fall times as small as 0.4 ns. The capacitance determined by pulsed x-ray illumination was in good agreement with the capacitance determined by pulsed optical laser illumination. The absolute responsivity was measured by comparison with the responsivity of a calibrated photodiode.