Accession Number : AD0894837

Title :   Surface Treatment and Sensitization of Semiconductor Photocathodes.

Descriptive Note : Final rept.,

Corporate Author : VARIAN ASSOCIATES INC PALO ALTO CA

Personal Author(s) : James, Lawrence W.

Report Date : APR 1972

Pagination or Media Count : 146

Abstract : It was shown that the long wavelength limit for efficient photoemission from cesium-oxide-coated III-V semiconductors is set by the height of an internal barrier, and not by the work function. The behavior of Cs2O as a low work function coating, including the interfacial barrier and the required Cs2O thickness, may be conveniently modeled by treating the Cs2O as an n-type semiconductor which forms a heterojunction with interface states when applied to a III-V semiconductor surface. The heterojunction parameters were shown to vary with the orientation of the III-V surface and with the composition of either the III-V material or the activation material. It was shown that the difference in photoemissive escape probabilities among different materials could be accounted for by the difference in heterojunction parameters. The phase diagram was calculated and liquid and vapor epitaxial growth techniques explored for several ternary III-V materials in order to find the material with the most favorable heterojunction parameters. It appears that InAsP is superior for thresholds of 0.97 micron or longer, while InGaAs (including GaAs) is best for cathodes with shorter threshold wavelengths. The surfaces of both of these materials were prepared by heat cleaning near the congruent evaporation point in an ultrahigh vacuum. A considerable improvement in photocathode sensitivity was obtained over a broad spectral range.

Descriptors :   *SEMICONDUCTORS), (*PHOTOCATHODES, (*INFRARED IMAGE TUBES, SEMICONDUCTOR DEVICES), INFRARED DETECTORS, SENSITIVITY, SURFACE PROPERTIES, BARRIER COATINGS, PHASE STUDIES, PHASE DIAGRAMS, EPITAXIAL GROWTH, PHOTOELECTRIC EFFECT, LIQUIDS, TRANSPORT PROPERTIES, ELECTRONS, EXCITATION, DIFFUSION, DOPING, CESIUM COMPOUNDS, OXIDES, SUBSTRATES, GALLIUM ARSENIDES, INDIUM COMPOUNDS, ARSENIC ALLOYS, ALUMINUM ALLOYS, ANTIMONY ALLOYS, BAND THEORY OF SOLIDS, THEORY.

Subject Categories : Electrooptical and Optoelectronic Devices
      Infrared Detection and Detectors

Distribution Statement : APPROVED FOR PUBLIC RELEASE