Shot noise in X-ray measurements with p-i-n diodes

The importance of shot noise is considered for situations in which p-i-n diodes monitor x-ray radiation. An expression for shot noise is derived in terms of the photon energy, the pair creation energy of the diode material, and the photocurrent. Statistical analysis shows that the Fano factor can be neglected for noise calculations. A lock-in amplifier measured the low frequency photocurrent noise from an unbiased silicon p-i-n photodiode that monitored radiation in the range of 6–16keV at a synchrotron beamline. With ordinary electronic amplification and shielding, shot noise dominated other noise sources for photocurrents exceeding about 5pA.