Hydrogen Induced Passivation and Generation of Defects in Polycrystalline Silicon

Abstract

The time and temperature dependence of defect passivation in undoped polycrystalline silicon was examined. At long passivation times the spin density saturates and the saturation value exhibits a strong dependency on the hydrogenation temperature. Hydrogen in undoped polycrystalline silicon diffuses in the positive charge state donating electrons. This causes an increase of the in situ electrical conductivity σP measured during the exposure of poly-Si to monatomic H. At long exposure times σP decays exponentially. Hall-effect data reveal that the Fermi energy shifts towards the valence band and the majority carriers 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.