Linearity of the Photocurrent Response with Light Intensity for Silicon PIN Photodiode Array

Among important parameters of photodetector arrays for medical imaging applications is the detector photo-response linearity with radiation flux. This paper addresses the above issue for the back-illuminated, thin pin photodiode arrays built on 75-mum thick single silicon dies. The features of the arrays include high quantum efficiency, fast signal rise time, very small AC and DC crosstalk (~0.01%) within the spectral range 400 to 800 nm, very low leakage currents and high shunt resistance (>10 GOmega). The photo-sensitivity linearity was found to be better than 0.01% within the spectral range from 450 to 1000 nm and in the range of input light fluxes above ~1 nW/pixel. For lower light fluxes, the nonlinearity of the photo-sensitivity was smaller than the noise current of the array pixels and different methods should be applied to provide measurements with an accuracy of better than 0.1%. This work also gives an estimate for the theoretical limit for the sensitivity linearity measurements.