Investigations of the Electrical Neutralization and Bonding Mechanisms of Shallow Impurities in Silicon Grain Boundaries

Interactions between shallow acceptors (B, Al, Ga and In) and hydrogen in polycrystalline Si are investigated. The bonding mechanisms involved in the acceptor neutralization process at grain boundaries are examined using microanalytical techniques. Differences in the incorporation of molecular and atomic hydrogen, and corresponding variations in electrical passivation at grain boundaries, are observed. Low-temperature Auger difference spectroscopy confirms Si-H bonding to dominate B, Ga and In-doped cases, with no direct acceptor-hydrogen bonding. Al-rich grain boundaries show H-complex and hydroxyl bonding. The data confirm chemical bond strength trends with B less than Ga less than In. Volume-indexed Auger electron spectroscopy is utilized to compare bonding and H-distributions in B- and Al-rich grain boundary regions.