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Radiation and Charge Injection in Al203 Using New Techniques.

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Final rept. 18 Dec 74-16 Dec 75,

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Optical transmission of unbacked thin films of thermally grown SiO2 films was measured in the vacuum UV. The absorption data indicate a bandgap of 8.0 or - 0.2 eV for SiO2, and this value is confirmed by measurements of electron and hole photoconductivity and positive charging thresholds in MOS samples. Coincidence of the absorption and hole photoconductivity thresholds provides evidence that the uppermost valence levels in SiO2 form a band, perhaps quite narrow, and most likely are dominated by oxygen 2 ppi and silicon 3d atomic orbitals. Vaccum ultraviolet radiation studies of steam-grown SiO2 samples with different annealing temperatures show a rather sharp minimum in hole trapping at 1000 C. The results indicate the presence of at least two trap species whose densities vary oppositely with anneal temperature. A reasonable fit to the experimental results is obtained using a two-trap model, with trap cross sections of 1.04 x 10 to the -13th power sq cm and 6.5 x 10 to the -15th power sq cm. The former is believed to be associated with a species that diffuses into the oxide, particularly at high anneal temperatures, and the latter is associated with intrinsic interface trapping. Corona discharge experiments are inconsistent with the VUV results in that a montonic increase in hole trap density with anneal temperature is observed. This is tentatively explained by the possible inability of this technique to fill traps with certain energy levels and spatial locations. Included in this report is a summary of previous work on Al203 which is described in earlier technical reports issued under this contract. AUTHOR

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  • Solid State Physics

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