Back-illuminated photodiodes for multislice CT: an estimation of temporal and spatial properties by carrier diffusion modeling

Randy P. Luhta; Rod Mattson; Narayan Taneja; Peter Bui

doi:10.1117/12.534626

6 May 2004 Back-illuminated photodiodes for multislice CT: an estimation of temporal and spatial properties by carrier diffusion modeling

Randy P. Luhta, Rod Mattson, Narayan Taneja, Peter Bui

Author Affiliations +

Proceedings Volume 5368, Medical Imaging 2004: Physics of Medical Imaging; (2004) https://doi.org/10.1117/12.534626
Event: Medical Imaging 2004, 2004, San Diego, California, United States

Abstract

A back illuminated photodiode (BIP) has been developed for multislice CT which enables a CT scanner to be made with a large number of slices. Light absorbed on one surface of the photodiode generates charge carriers which diffuse through the silicon bulk to charge collection anodes on the opposite side. It is this minority carrier diffusion through the bulk which governs the spatial and temporal properties of the photodiode. The diffusion of carriers in the silicon is described by a partial differential equation (PDE) which can be solved numerically for a given geometry. Modeling carrier diffusion allows one to determine the risetime and response profiles for a given photodiode design without the expense of fabricating an actual device. The PDE for carrier diffusion has been solved for different BIP geometries using the Matlab PDE toolbox. This software uses the finite element method in two dimensions. Risetime and response profiles have been simulated for the same geometries as BIP devices that have been fabricated. The simulation results are in good agreement with the measurements done on actual devices. New geometries are also simulated to show how the BIP can be optimized.

Citation Download Citation

Randy P. Luhta, Rod Mattson, Narayan Taneja, and Peter Bui "Back-illuminated photodiodes for multislice CT: an estimation of temporal and spatial properties by carrier diffusion modeling", Proc. SPIE 5368, Medical Imaging 2004: Physics of Medical Imaging, (6 May 2004); https://doi.org/10.1117/12.534626

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