Modeling Charge Diffusion from Proton-Induced Ionization Tracks in Silicon Photodiode Arrays

Date of Award

Summer 8-1982

Document Type


Degree Name

Master of Science (MS)



Committee Director

Jacob Becher

Committee Member

G. E. Copeland

Committee Member

G. S. Khandelwal

Committee Member

R. L. Kernell


We are modeling the combined problem of generation and collection of charge carriers created during passage of energetic protons through a silicon photodiode array. We have also experimentally obtained pulse-height distributions of noise charge collected during exposure of a Digicon-type diode array to 21 and 75 MeV protons. It is shown that the magnitude of charge collected by a diode from each proton event is determined not only by diffusion, but by statistical considerations involving the ionization process itself. Utilizing analytical solutions to the diffusion equation for transport of minority carriers, together with the Vavilov-Landau theory of energy-loss fluctuations in thin absorbers, we present simulations of the pulse-height spectra which follow the experimental distributions fairly well, and provide us with an estimate for the minority carrier diffusion length Ld of 90 microns.


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