HYDROGEN-INDUCED PASSIVATION AND GENERATION OF DEFECTS IN POLYCRYSTALLINE SILICON

The time and temperature dependence of defect passivation in undoped p olycrystalline silicon was examined. At long passivation times the spi n density saturates and the saturation value exhibits a strong depende ncy on the hydrogenation temperature. Hydrogen in undoped polycrystall ine silicon diffuses in the positive charge state donating electrons. This causes an increase of the in situ electrical conductivity sigma(P ) measured during the exposure of poly-Si to monatomic H. At long expo sure times sigma(P) decays exponentially. Hall-effect data reveal that the Fermi energy shifts towards the valence band and the majority car riers change from electrons to holes. The observed type conversion is due to the diffusion of excess hydrogen from the plasma since it does not occur during exposure: to other species such as oxygen.