SURFACE ACTIVATION OF PHOTOCONDUCTIVE PBS FILMS

Photoconductive PbS films -after being exposed to an oxygen atmosphere at low temperature (T < 200 degrees C) or to chemical oxidizing reage nts at room temperature- exhibit a considerable increase of the ratio [dark resistance/illuminated resistance (photoconductive resistance)]. This fact is related to the generation of surface states which are pr oduced by a reversible chemisorption of oxygen at the surface of the P bS grains. Surface acceptor states are formed in the n-type polycrysta lline PbS grains and a positive space-charge is generated at the grain boundaries. This barrier greatly reduces the film conductivity but if enough oxygen is chemisorbed, conductivity increases again and materi al turns into p-type. In this paper a strong oxidizing method in ozone atmosphere for PbS photoconductive detectors is proposed. The employe d method and equipment are described and results of structural and ele ctrical characterization of PbS films are given.