ELECTRICAL-CONDUCTIVITY OF AMORPHOUS-CHALCOGENIDE FILMS IN AS-SE-SB SYSTEM

The dc electrical conductivities of undoped and Mo-doped amorphous As-Se-Sb films of thickness 600 angstrom were measured over a range of temperature from 90 to 290 K. The films were prepared by resistance heating and vacuum evaporation. DC conductivities were measured by a four-point technique as a function of temperature from 90 to 290 K. Samples were in normal atmosphere during conductivity measurements. An As26Se60Sb14 film had conductivities from 10(-8) to 10(-10) S cm-1 and the conduction is due to hopping conduction at temperatures > 225 K and to two-dimensional variable-range hopping at temperatures < 185 K. Both mechanisms coexist at temperatures from 185 to 225 K. Mo-doped 23 at.% amorphous As40-xSe60Sbx (x=3-14 at.%) films had a conductivity of 10(2)-10(3) S cm-1 and had no measureable temperature dependence. This temperature invariance is interpreted in terms of the metal-insulator transition.