POSITRON TRAP SITES IN THE NATIVE-OXIDE FILM GROWN ON A HYDROGEN-TERMINATED SILICON SURFACE

Positron behavior in thin native oxide layers grown on an initially hydrogen-terminated Si(100) surface was investigated and correlated with the chemical structure of the layers determined using Fourier-transform infrared absorption attenuated total reflection spectroscopy, and x-ray photoelectron spectroscopy. Hydrogen termination of the Si surface by 4 vol % HF treatment gave rise to a narrower Doppler-broadened positron-electron annihilation line than that of bulk Si. By a process of oxidation in pure water very thin (up to 7.8 angstrom) layers were grown on the H-terminated Si. The Doppler broadening of annihilations from the Si surface was seen to increase monotonically with thickness away from the value seen for amorphous bulk SiO2. The positronium fraction was monitored throughout but was found to be independent of the oxidation duration. It was found that the chemical structure of the surface, in particular the oxidized Si-OH bond, was correlated with the positron annihilation mode and to the level of observed Doppler broadening.