Hydrogen-Induced Generation of Acceptorlike Defects in Polycrystalline Silicon

The in situ electrical conductivity ${\sigma }_P$ of undoped polycrystalline Si was measured during exposure to monatomic H at high temperatures. Initially, ${\sigma }_P$ increases due to electrons contributed by in-diffusing H donors. At long exposure times ${\sigma }_P$ decays exponentially. Hall-effect data reveal that the Fermi energy shifts towards the valence band and the majority carriers change from electrons to holes indicating the creation of acceptor states. The observed type conversion is due to the diffusion of excess H from the plasma since it does not occur during exposure to other species such as oxygen. The acceptor creation is thermally activated with 1.62 eV and the acceptors anneal with an activation energy of 2.75 eV.