A. G. U. Perera
Department of Physics and Astronomy, Georgia State University, Atlanta,
GA 30303
INTRODUCTION
Photoemission was discovered by Heinrich Hertz (1857-1894) in
1887. He observed that the spark production between two electrodes can be
enhanced by exposing the negative electrode to ultraviolet light. After the
electron was discovered by Thomson, observed photoelectric effects could be
explained as electron emission induced by radiation. The photoelectric
emission, in which a photo-generated carrier escape the host material and become
a free carrier can be listed as an external photo-effect (or external photo-emission).
The most widely known, external photoemission is the Einstein's demonstration
of the classic photoelectric effect,
suggesting that the photoelectric effect is a quantum effect, for which he was
awarded the Nobel Prize. After Einstein's ideas were accepted, photoemission
studies were carried out to understand the behavior of different materials.
Fowler and co-workers studied threshold wavelengths, quantum efficiencies, and
spectral responses, stimulating the interest for further studies. One of the
detailed description of photoemission is given by A. H. Sommer in his book
``Photoemissive Materials" in 1968. Most of the photoemissive work up to
early 50's was concentrated on the external photoemission. A more recent review
of photoemission is given by Escher in the volume 15 of Semiconductors and
Semimetal series.
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