Experimental and theoretical studies of the variation in photoresponse of the Si: Cs-0 negative electron affiity (NEA) photocathode with thickness of the Cs-0 overlayer and acceptor concentration in the Si bulk, are reported. Resonance transmission peaks in the variation of photoyield with increasing overlayer thickness are predicted and observed. From a comparison of theoretical and experimental curves, the electron attenuation length in the overlayer is estimated to be about 50.& The theoretical analysis indicates that the optimum overlayer is metallic with a carrier concentration of about 2 x 1021 cm-3, varying slightly with bulk acceptor concentration. As a consequence of resonance transmission, the overlayer may enhance electron emission beyond expectations based solely on its workfunction-lowering effect.

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Electric field enhancement of photoemission from negative-electron-affinity surfaces on silicon and GaAs has been studied. It is shown that the electric field increases the escape probability and does not change the spectral response of negative-electron-affinity surfaces. The results are explained by assuming a simple surface potential barrier together with work function lowering by the Schottky effect.

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The design of scientific image sensors has not progressed as rapidly as developments in the technology could have permitted. This has been a consequence of an incorrect perception by manufacturers that the scientific market was insufficiently large to justify the required investment which, in turn, has lead to the use by many scientific customers of 'do-it-yourself' design and foundry solutions to their imaging needs. This paper will introduce the basic features of the new generation image sensor and will describe the design of these devices.