Prediction of Dose Gradients and Their Effects on Semiconductors.
GENERAL ELECTRIC CO PHILADELPHIA PA RE-ENTRY SYSTEMS DEPT
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The absorbed dose in a material near a boundary with a dissimilar material may differ considerably from the dose in the bulk material. The peak dose near the interface can be more than a factor of ten greater than the bulk dose. The dose distribution is determined by the energy deposition of the secondary electrons liberated in the material by the photon radiation, and the gradient arises from the differences in the secondary electron production and transport properties of the two materials. A Monte-Carlo model was developed for the predictions of the dose distribution and current distribution at a planar interface, and predicted results show excellent agreement with available experimental data. An examination of the effects of the dose gradients on the transient response of semiconductors shows that diode photocurrents are strongly influenced by dose gradients, and can be increased by as much as the surface dose ratio. As a first approximation, the effect can be accounted for at low dose rates by using existing device electronic models and adjusting the photocurrent value. Bulk semiconductors exhibit an induced emf due to dose gradients, a phenomena not encountered under uniform dose irradiation. Author
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