A metal/Insulator/semiconductor (MIS) photocathode

A field-assisted photocathode based on the metal/alumina/ silicon (MAS) structure is described. Emission currents as large as 10 percent of the photoelectric current in the silicon have been demonstrated with spectral response only limited by the bandgap of the semiconductor. This suggests that MIS structures employing narrower band-gap semiconductors would be useful when response beyond 1 µm is desired. The MAS time response to a change in light is inversely proportional to the light level. Under illumination equivalent to moonlight (2 × 10¹¹absorbed photons/cm²/s) a time response of 4 s has been measured. In the simple planar structure described, charge spreading occurs in the inversion well. For imaging, a more complex structure is required.