''SOME STUDIES ON THE PHYSICAL PROPERTIES OF CHEMICALLY AND THERMALLY EVAPORATED BISMUTHINITE (Bi2S3) FILMS"

Abstract

The present work presented the results of studies of the structure and composition of the deposited bismuth trisulfide thin films and the relevance of their optical and electrical characteristics. Also, it is to investigate the effect of the thermal treatment on the structure, optical and electrical properties of the various films. The Bi 2S3 films prepared by two deposition techniques [thermal evaporation and chemical deposition]. Two methods were used to determine the film thickness. All the films are examined before and after their thermal treatment, by X-ray diffraction and scanning electron microscope. The results could be summarized as follows :- 1- The structure of the thermally and chemically deposited Bi2S3 films was studied by scanning electron microscopy and X-ray diffraction. From X­ ray analysis, the films obtained arc nearly stoichiometric. A very well defined transition to the crystalline state is observed in both thin film and powder samples after annealing in air. The thermal stability of the powder samples shows an exothermic pe<lk ncar 231 "C. This is consistent with the amorphous to crystalline transition in chemically deposited Bi 2S3

(powder) samples, as already indicated to the X-ray diffraction spectra. The crystallite size was estimated using scherrer formula. The electron micrographs of the non-heated layers demonestrate the increase in the grain size with increasing of dipping time. After heating the samples, the dimensions of the crystallites are not uniform and an aggregate of islands with overgrowth scattered here and there. The rate of deposition and the terminal thickness depend sensitively on the temperature of the deposition.

2- For optical measurements, Bi2S3 thick films were prepared by the two

" techniques. The optical constant (n and k) were determined from the transmission and reflection spectra.