Silicon may be activated to negative electron affinity to give an efficient electron mulitplier or photocathode. Thinned self-supporting wafers have been prepared, and the effects of doping level, wafer thickness and back surface treatment have been studied. The results showed that the back surface recombination velocity can be improved to an acceptable value, leading to the efficient emission of electrons and consequently high values of transmission photoemission and secondary electron multiplication.The use of anti-reflection coatings to selectively enhance the response in a particular waveband is also described. Since silicon normally has a high reflection coefficient, the use of these coatings has lead to a considerable improvement in white light sensitivity, and cathodes with a sensitivity as high as 1000 FA lm-1 have been prepared.

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