Investigation On Structural And Physical Properties Of Some Selenium Rich Semiconducting Glasses

Abstract

The chalcogenide glasses form a recognized group of inorganic glassy materials having newlinemajor constituent as one or more of the chalcogens like Sulphur (S), Selenium (Se) and newlineTellurium (Te) except oxygen. The selenium has been used as base chalcogen element, due to its newlineexcellent glass forming ability, to form chalcogenide glasses. However, poor thermal stability, newlinelow glass transition temperature, high level of intrinsic defects and low photo sensitivity limit its newlinewide applicability in devices. In order to improve the functionalities some other elements, such newlineas Ge, As , Sn, Pb, Sb, Bi, In Si, P, B, Ag, Ga, Na and lanthanides have been used as additives in newlineselenium or selenium containing alloys. newlinePhysicist B.T. Kolomiets and Chemist N.A. Gorjunova [Kolomiets and Gorjunova, 1955] newlinefrom Ioffe s Physical and Technical Institute (St. Petersburg) discovered the semiconducting newlineproperties of Chalcogenide glasses during surveying of photoconductivity of these materials. At newlinethe same time, the researchers at Leningrad State University studied the chalcogenide glass from newlinechemical points of view, i.e., as ion-conducting and infrared transmitting materials. Generally, newlinethese amorphous materials are p-type semiconductors. The reason for the same is considered to newlinebe twofold: (i) the carrier life time, excited above the Fermi level (electrons), is small as newlinecompared to below the Fermi level (holes) as determined with photoconductivity experiments, newline(ii) Seeback coefficient is positive. The disorder induced localized states extended into the newlineforbidden band gap have significant effect on the electrical and optical properties of these glassy newlinematerials. These glasses as constitute have large and heavy atoms which shift phonon energy to newlinethe lower value or to the longer wavelengths, as a consequence the transparency window of these newlinematerials extends to the far-infrared. This low phonon energy or transparency in far infrared newlinemakes the chalcogenide glasses attractive as infrared optical material. newline