Hydrogen interactions with cavities in helium-implanted silicon

Hydrogen interactions with microscopic cavities in Si were quantitatively characterized in thermal-release experiments. Closed internal cavities were formed by He-ion implantation and annealing and were characterized by transmission-electron microscopy. The isotopes protium ${(}^1$H) and deuterium (D) were introduced by ion implantation or heating in ${\mathrm{H}}_2$ gas. During temperature ramping the redistribution and release of D were monitored by nuclear-reaction profiling, and the bonding of ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ was selectively examined by infrared absorption spectroscopy. By exploiting the properties of closed internal surfaces this study determined the Si-H bond energy for surface monohydrides, the result being 2.5±0.2 eV. Hydrogen bonded to the internal surfaces was found to lie several tenths of an eV lower in energy than ${\mathrm{H}}_2$ gas and H trapped at lattice defects. The oxidized external surface of the Si specimens did not detectably impede H release, implying an efficient recombination process at the Si-${\mathrm{SiO}}_2$ interface for which possible mechanisms are considered.