This research was supported by a Grant-in-Aid of Research from the National Academy of Sciences, administered by Sigma Xi, the Scientific Research Society and by the Tektronix Corporation.
Monte Carlo method, Charge coupled devices, Electrons -- Scattering
The potential well in back-illuminated charge-coupled devices (CCDs) does not reach all the way to the back surface. Hence, light that is absorbed in the field-free region generates electrons that can diffuse into neighboring pixels and thus decreases the spatial resolution of the sensor. We present data for the charge diffusion from a near point source by measuring the response of a back-illuminated CCD to light emitted from a submicron diameter glass fiber tip. The diffusion of electrons into neighboring pixels is analyzed for different wavelengths of light ranging from 430 to 780 nm. To find out how the charge spreading into other pixels depends on the location of the light spot; the fiber tip could be moved with a piezoelectric translation stage. The experimental data are compared to Monte Carlo simulations and an analytical model of electron diffusion in the field-free region. The presented analysis can be used to predict the charge diffusion in other back-illuminated sensors, and the experiment is universally applicable to measure any type of sensors.
Ralf Widenhorn, Alexander Weber-Bargioni, Morley M. Blouke, Albert J. Bae and Erik Bodegom, (2010) "Charge diffusion in the field-free region of charge-coupled devices", Opt. Eng. 49, 044401.