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CONTACT PROPERTIES AND RELATED CONDUCTION PHENOMENA IN INSULATING CADMIUM SULFIDE.
Technical rept. 1 Oct 64-1 Mar 66,
MASSACHUSETTS INST OF TECH CAMBRIDGE PHOTOCONDUCTIVE SEMICONDUCTORS AND DEVIC ES LAB
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The static distribution of the electric field in thin insulating crystals of DcS provided with various electrodes was investigated. It was found that, when non-injecting electrodes were used, contact barriers were formed which have the nature of the usual Schottky barriers known to exist on high-conductivity CdS. The square of the barrier thickness is linear in the applied voltage, and the barrier potential is related to the metal work-function, the electron affinity of CdS, and the Fermi level depth, as predicted by the simplest contact theory, without having to resort to surface states. The barrier thickness, which for insulators cannot be measured by any of the standard semiconductor procedures, was derived from the measurement of a fast-pulse photoeffect. A pulse photoeffect model was developed that successfully explains the results in terms of contact barriers. The barrier space-charge density can be related to the bulk density of centers. The barrier photoeffect model in CdS is dependent on the presence of native defects of relatively high density and electron cross-section. The properties of these centers are in agreement with previous reports. Slow sensitizing centers were also investigated, and their cross-section is in good agreement with previously-reported values. The results indicate how to prepare contacts that approach the flat band condition. This is shown to be important for accurate resistivity measurements on thin crystals. Author
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