Recent studies on photoconductive thin films of binary compounds

• Published in: Synthetic metals Vol. 99; no. 1; pp. 45 - 52
• Main Authors: Bernède, J.C., Pouzet, J., Gourmelon, E., Hadouda, H.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 29.01.1999; Amsterdam Elsevier Science; New York, NY
• Subjects: Binary compounds; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Exact sciences and technology; MX 2 films; Photoconduction and photovoltaic effects; Photoconduction and photovoltaic effects; photodielectric effects; Photoconductive thin films; Physics; MX 2 films; Binary compounds; Photoconductive thin films; Buffer layer; Grain boundaries; Annealing; Inorganic compounds; Electrical conductivity; Molybdenum sulfides; Transition element compounds; Crystallization; Thin films; Reviews; Molybdenum selenides; Tungsten sulfides; Property structure relationship; Photoconductivity; Tungsten selenides
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/S0379-6779(98)00199-4

In this paper a review of recent progress achieved in the domain of MX 2 films (M=Mo, W; X=Se, S) is presented. The MoS 2 is essentially discussed. It is shown that the emerging interest in the use of MX 2 thin films as absorbing layer in photovoltaic cells has induced significant improvements of the crystalline and optoelectrical properties of these films. Some years ago the films obtained were crystallized in the 2H-MoS 2 structure but the size of their crystallites was small and the samples were poorly photoconductive. Recently many works have shown that, whatever the deposition technique used, textured films with large grains and good photoconductive properties could be obtained when a thin nickel layer is used. During the post annealing treatment, this thin nickel layer diffuses all over the thickness of the films. It is proposed that systematically the crystallization process of MX 2 films is a two-step process. The primary crystallization corresponds to small crystallites formation and the secondary crystallization corresponds to large ordered domains growth by coalescence of the small crystallized domains. This secondary crystallization process is facilitated by the presence of Van der Waals surfaces parallel to the plane of the substrate. Moreover, this effect is strongly improved in the presence of nickel which allows the obtention of high quality films. The electrical properties of these films are interpreted with the help of grain boundary theories.