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Vacancy Equilibration of Photoconductors during Sintering

IP.com Disclosure Number: IPCOM000096135D
Original Publication Date: 1963-Jan-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Berkenblit, M: AUTHOR [+3]

Abstract

CdSe has been demonstrated to lie an incongruently vaporizing compound. By this it is meant that when CdSe, stoichiometric to within the limits its elemental constituents may Ge weighed prior to synthesis, is heated in air, inert gas or vacuum it tends to become selenium deficient up to 1% or thereabouts with respect to Cd/Se molar ratio. Such a selenium deficiency implies that a donor level of Se will be present in fabricated photoconductors of the order of 10,000 parts per million. If these donors are not in some way compensated, the resultant photoconductor is useless as a device. This is because it exhibits dark and light conductivities of similar magnitudes. In other words, the photoconductors are insensitive.

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Vacancy Equilibration of Photoconductors during Sintering

CdSe has been demonstrated to lie an incongruently vaporizing compound. By this it is meant that when CdSe, stoichiometric to within the limits its elemental constituents may Ge weighed prior to synthesis, is heated in air, inert gas or vacuum it tends to become selenium deficient up to 1% or thereabouts with respect to Cd/Se molar ratio. Such a selenium deficiency implies that a donor level of Se will be present in fabricated photoconductors of the order of 10,000 parts per million. If these donors are not in some way compensated, the resultant photoconductor is useless as a device. This is because it exhibits dark and light conductivities of similar magnitudes. In other words, the photoconductors are insensitive.

Techniques have been employed to compensate these undesirable donor levels. These include post treatment of fabricated photoconductors in S, Se or O(2) atmospheres at low temperatures, low relative to the maximum temperature in a time -temperature sintering cycle, or to sinter the photoconductor in an oxygen-nitrogen atmosphere. Neither of these methods is, however, completely desirable. In the first method, it is impractical in a reasonable time period to completely backfill all of the selenium vacancies. The net effect is to obtain a photoconductor metastable with respect to its Se vacancy content and one which tends to fill these vacancies with oxygen from the air over long time periods. This results in a change of electrical characteristics, the latter process being termed, aging, Furthermore, this procedure is difficult to effect reproducibly and one expects to obtain spreads in electrical characteristics gr...