Formation of chalcogen containing plasmas and their use in the synthesis of photovoltaic absorbers

Chalcogen-containing plasmas were used to convert indium, copper–indium, and copper–indium–gallium films into their respective chalcogen-containing phases. An argon plasma was used to activate either hydrogen sulfide or elemental selenium vapor. The article describes the inductively coupled plasma setup and its characterization using optical emission spectroscopy. The kinetics of selenide/sulfide formation were examined as a function of time and temperature. The thin films were characterized using x-ray diffraction, optical transparency, and scanning electron microscopy. In all cases the use of the plasma dramatically enhanced chalcogen reactivity. Indium films were completely converted to β-In2S3 at 250°C by plasma processing, while no evidence of this phase was observed in films treated thermally at 350°C. The use of plasma enabled the complete conversion of Cu–In and Cu–In–Ga precursors to their ternary and quaternary chalcopyrite phases, respectively, at 350°C in less than 1h using chalcogen partial pressures <1Pa.