Surface Treatment and Sensitization of Semiconductor Photocathodes.
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1972
- Accession Number
- AD0894837
Entities
People
- Lawrence W. James