Fractionation of Antimony Triselenide

Abstract

Optical density, dark conductivity, and photoconductivity of evaporated antimony triselenide thin films were studied as a function of deposition conditions. The film properties may vary appreciably with both source temperature and time at which the deposition is made. Initial deposits exhibit abnormal bandgap energies, as high as 1.7 eV with a source operated 20 deg below the Sb2Se3 melting point. The bandgap energy decreases monotonically with time during a long evaporation, finally approaching a constant value in the 1.1–1.2 eV range if the boat is maintained at or above the Sb2Se3 melting point (611 °C). The data suggest that initially stoichiometric Sb2Se3 fractionates during the early stages of evaporation, the Se-Sb ratio of the melt decreasing until a composition range producing films with constant bandgap energy is reached. Spectrographic analyses of different fractions from the vapor stream support this explanation.

Chemical inhomogeneity in zinc telluride thin films prepared by thermal evaporation

“…Fractionation continues throughout the evaporation with rate decreasing as the concentration of Zn in the boat decreases. A similar trend was observed earlier in the evaporation of Sb 2 Se 3 using effusive-types of evaporation sources [17]. At a given temperature, the vapor pressure of Se is much larger that that of Sb [16].…”

“…At a given temperature, the vapor pressure of Se is much larger that that of Sb [16]. Efstathiou et al [17] observed that when the evaporation temperature was kept constant (as in present work), the atomic ratio of Se/Sb decreased with time. They commented that the material in the boat was initially stoichiometric Sb 2 Se 3 , fractionates during early stages of evaporation until a composition range of approximately constant value is reached.…”