Thin GaAsxSy films are deposited on Mo substrates by reactive radio-frequency sputtering of a polycrystalline GaAs target by adding H2S to the discharge gas (Ar). We used optical emission spectroscopy and mass spectrometry to study the As-S exchange reaction activity during sputter deposition as a function of different sputtering parameters. The analysis of electrical and photoelectrical properties of the Schottky junctions realised, Mo/GaAsS/Au, shows that with an increase in sulfur concentration there is : an improvement of the gold/semiconductor interface (decreasing interface index and increasing barrier height); a significant lowering of grain boundary electrical activities. We have thus prepared a ternary polycrystalline compound GaAsxSy which presents promising electrical and photoelectrical properties, even for films as thin as a few microns with grains of about one micron.