LOW TEMPERATURE INFRARED PHOTOCONDUCTORS.

The first results obtained in studies directed toward the development of an infrared photoconductive multiplier are summarized. This device, which is a solid state analog of the secondary emission multiplier for photoelectrons, is to be a multi-layered structure consisting of a suitable photoconductor followed by alternate layers of wide and narrow band gap semiconductors. Carriers optically excited in the photoconductor are accelerated in the first wide band gap semiconductor layer. When these enter the narrow band gap material, their excess energy is lost in production of electron-hole paris by intrinsic impact ionization. The additional carriers so produced are accelerated in the second wide band gap layer to produce additional multiplication in the second narrow band gap layer, and so on. The problem considered in the present report is the choice of suitable materials for the wide band gap layers. One such material is amorphous selenium. Holes photoexcited in a photoconductor can be injected into and transported through Se layers. Electrons are not transported. Other possible wide band gap materials include silver chloride and cadmium sulfide. These have not yet been extensively investigated. The problem of accelerating carriers to high energies in the wide band gap material will receive primary attention in the next phase of the work. Author