Interference-enhanced photoemission

In order to study the enhancement of the ir response of photocathodes, a model describing the effects of absorption and interference within a semiconductor photocathode supported by a reflecting metallic substrate is developed. It is shown that the addition of a dielectric spacer between the metallic substrate and the cathode emitter to give a combined optical thickness of quarter wavelength enhances the quantum efficiency of photocathodes over a wider spectral range, and extends their maximum response toward the ir. With the choice of dielectric spacer thickness established by an optimum photocathode thickness, a broad spectral response is obtained with reasonably thin dielectric and thin photocathode layers. The absorption coefficient very strongly determines the degree of enhancement which is observed to increase rapidly at the longer wavelengths.