PLASMA-ASSISTED 2-STAGE SELENIZATION PROCESS FOR THE PREPARATION OF SELENIDE SEMICONDUCTOR THIN-FILMS USING ELEMENTAL SELENIUM VAPOR

A plasma assisted two stage selenization process using elemental selenium vapor is demonstrated for the preparation of selenide semiconductor thin films. Vacuum evaporated copper films are selenized using the vapor of elemental selenium which has been ionized by a radio frequency plasma. This enhances the reaction kinetics by modifying the availability and ionization state of Se(x) species present in the gas phase. In contrast to the H2Se selenization, the availability of the Se(x) species in the gas phase is not dependent on the kinetics of its reaction with the precursor. Formation of highly crystalline CuSe films has been observed at low temperatures (250-degrees-C) within 2-5 min. CuSe films show large (almost-equal-to 2-5 mum) rodlike crystallites, with a highly oriented microstructure in plasma assisted growth as different from the small (less-than-or-equal-to 1 mum) coalescing grains in the polycrystalline films formed by the conventional selenization scheme. X-ray diffraction shows a threefold enhancement in the intensity of the (006) reflection of the hexagonal CuSe phase indicating the orientation of the c axis of the crystallites, normal to the plane of the film. The observed hexagonal CuSe growth phase is in agreement with the thermodynamics of copper selenium vapor reaction.