NEW METHOD FOR THE DEPOSITION OF AS2S3 THIN-FILMS

A relatively new method has been developed to prepare the thin arsenic trisulphide films at low temperatures, especially at room temperature . At this temperature, the deposition time required to produce good qu ality films is around 96 hr and an increase in bath temperature reduce s the deposition time down to 18 hr. The room temperature conductivity is of the order of 10(-9) ohm(-1) cm(-1) and the electrical conductio n is of the n-type. The X-ray diffraction studies showed the structure of the deposited films as consisting of crystallites of monoclinic As S with a background of large number of microcrystallites of As2S3. The structure remains more or less unaltered up to 200 degrees C and beco mes completely microcrystalline at higher temperatures. The grain size s for AsS and As2S3 phases have been determined using the Scherrer's r elation and typically they are 251.93 and 26 Angstrom, respectively. T he SEM observations for as-deposited sample showed well-defined grains of the spherical and pyramidal shapes with a very large number of sma ll grained diffused crystallite background. The grain size has also be en computed and it matches fairly with the XRD observations. The sampl es heat treated above 200 degrees C, showed microcrystalline As2S3. Op tical studies showed the absorption edge at 2.35 eV for as-deposited A s2S3, while it is found to be shifted towards still higher energy side for heat treated samples. The observed electronic transition is of th e band-to-band direct type.