15 June 2006 Analysis of the charge collection process in pnCCDs
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At MPI Halbleiterlabor, pnCCDs have been continuously developed to improve readout noise, readout speed, charge transfer efficiency and energy resolution. Pixel sizes of 75μm, 51μm and 36μm were realized in addition to the original 150μm pixel design. Reduction of the pixel size evidently changes the electric fields in the pixel structure. This leads to the question of how scaling of the pixel size affects the charge collection at subpixel dimensions. We used the "mesh-method" to measure the amount of signal charge deposited in a pixel depending on the position of X-Ray photon incidence within the pixel. In this experiment, a mesh with a rectangular hole pattern was mounted above the entrance window or structured front side of the detector. A slight rotation of the mesh ensures that every hole has a different position relative to the pixel below. It corresponds to scanning of a single pixel. Measurements were done with pnCCDs of 150μm, 75μm and 51μm pixel size at photon energies from 0.7keV to 5.4keV. We also used a setup with front side illumination of a pnCCD with 75μm pixel size to investigate the absorption of X-ray photons in the register structure of the device. Numerical simulations delivered results for signal charge distribution into pixels along the charge transfer direction. We analyzed the charge collection in a pixel and the absorption properties of the register structure with a spatial resolution below 5μm and could investigate the accuracy of numerical device simulations.
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N. Kimmel, N. Kimmel, R. Hartmann, R. Hartmann, P. Holl, P. Holl, N. Meidinger, N. Meidinger, R. Richter, R. Richter, L. Strüder, L. Strüder, "Analysis of the charge collection process in pnCCDs", Proc. SPIE 6276, High Energy, Optical, and Infrared Detectors for Astronomy II, 62760D (15 June 2006); doi: 10.1117/12.673460; https://doi.org/10.1117/12.673460

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