Electron and Proton Damage Coefficients in Low-Resistivity Silicon

Electron and proton damage coefficients have been determined for low resistivity silicon based on minority-carrier lifetime measurements on bulk material and diffusion length measurements on solar cells. Major observations made and conclusions reached are the following. 1) Diffusion-length damage coefficients (KL) increase with decreasing resistivity (ρ) for boron-doped silicon. For 0.5-, 1.0-, and 2.5-MeV electron bombardment, empirical fits to experimental data can be approximately expressed as KL ∝ ρ-2/3 for 0.1 ≤ ρ ≤ 20 ohm-cm. For 10-MeV proton bombardment, an empirical fit of the form KL ∝ ρ-0.44 was found to describe the data reasonably well. 2) The dependence of damage coefficient on resistivitycanbe qualitatively accounted for quite well using a two-level Hall-Shockley-Read model. 3) Damage coefficients for solar cells were observed to be larger than their bulk-material counterparts. 4) Bulk samples and solar cells prepared from float-zone material were generally observed to be more radiation tolerant than their Czochralski counter-parts at all resistivities examined. 5) No dependence of damage coefficient on dislocation density was apparent for 0.1 ohm-cm bulk samples and solar cells.