AQUEOUS PRECIPITATION AND ELECTRICAL-PROPERTIES OF IN2S3 - CHARACTERIZATION OF THE IN2S3 POLYANILINE AND IN2S3 POLYPYRROLE HETEROJUNCTIONS

The stability of indium sulphide aqueous supersaturated solutions at pH 2.50 and 25-degrees-C was investigated. Spontaneous precipitation proceeded at rates proportional to the solution supersaturation via a polynuclear mechanism and the phase formed was identified as In2S3. The absorption spectrum of In2S3 was measured from 1 90-800 nm and from the absorption threshold the optical energy gap was estimated to be E(o) = (1.8 +/- 0.1 ) eV. The thermal energy gap E(t) = (1.6 +/- 0.2) eV was determined from resistivity against temperature measurements and a thermopower coefficient S = - 100 muV K - 1 at room temperature was found. Finally, In2S3/polyaniline and In2S3/polypyrrole heterojunctions were prepared and from the investigation of their I-V characteristics, the values of the ideality factor, n, the saturation current density, J(o), and the effective barrier height, phi(B), were determined to be n = (15 +/- 2), J(o) = (38 +/- 7) A m-2 and (phi(B) = 0.56 eV for the polyaniline and n = (64 + 8), J(o) = (13 +/- 2) A m-2 and phi = 0.59 eV for the polypyrrole heterojunction.