Composition Effect on the Optical and Electrical Parameters of BixSe100−x Thermal Evaporated Films

A systematic study of the thermal, structural, optical and electrical properties of BixSe100-x, glasses (x = 5, 10, 15, 25 at %) were carried out. The bulk materials were prepared by the usual melt quenching technique then thin films were deposited by thermal evaporation under 10(-5) Torr vacuum. The DTA analysis indicated the dependence of the glass transition and crystallization temperatures on the compositions. The crystalline phases were identified using x-ray powder diffraction and scanning electron microscope techniques. The mechanism of the optical absorption followed the rule of direct transition. The optical energy gap decreases and width of localized states increases with increasing Bi content. The dependence of the electrical conductivity on the composition has been investigated. The sigma - T dependence for all considered compositions shows semiconductor materials behavior. The conduction phenomena of the investigated thin films proceeded through two distinct mechanisms. In the high temperature region the thermally activated conduction may be represented through the extended states. In the low temperature region (less thermally activated) can be represented by the hopping conduction through the localized states.