FORMATION OF SECONDARY IRON-SULFUR PHASES DURING THE GROWTH OF POLYCRYSTALLINE IRON PYRITE (FES2) THIN-FILMS BY MOCVD

Thin films of iron pyrite (FeS2) have been prepared on glass and glass y carbon substrates by low pressure metal organic chemical vapour depo sition (LP-MOCVD) using iron pentacarbonyl (Fe(CO)(5)) and di-tert.-bu tyldisulphide (TBDS) as precursors. The TBDS partial pressure was vari ed from 1 to 100 Pa for different iron pentacarbonyl partial pressures (0.25, 0.5 and 1 Pa) while all other parameters were maintained const ant. It was found that there is a critical TBDS-partial pressure of ab out 30 Pa for a deposition temperature of 475 degrees C, where a drast ic change in the layer properties occurs. Below this TBDS partial pres sure pyrrhotite type phases (Fe1-xS) will be formed although there is a sulphur precursor excess in the gas phase. If the layers contain pyr rhotite, the electrical properties of the FeSx-films are changed signi ficantly. The occurrence of the pyrrhotite phases does not depend on t he growth rate, hence it is not controlled kinetically. Therefore, the sulphur pressure above the growing pyrite film is the important param eter controlling the solid phase. The present investigation shows that , in order to prepare pyrite thin films of good electronic quality, on e has to take care to avoid the secondary sulphur-iron phases even in very small concentrations. (C) 1998 Chapman & Hall.