A large change in the number of Si-H bonds in boron-doped ([${\mathrm{B}}_2$${\mathrm{H}}_6$]/[${\mathrm{SiH}}_4$]=2 vol%) hydrogenated amorphous silicon during low-temperature (220 °C) annealing has been observed. The number of Si-H bonds as determined by Raman scattering, infrared spectroscopy, and from the optical gap showed a logarithmic decrease with anneal time to less than half after a 100-h anneal. It is shown that during long-anneal sequences hydrogen is transferred irreversibly from a bonded state into molecular ${\mathrm{H}}_2$ trapped in the samples. This has important implications for the determination of H-diffusion coefficients by nuclear techniques such as secondary-ion mass spectroscopy or elastic-recoil detection analysis.

• Received 29 May 1990

DOI:https://doi.org/10.1103/PhysRevB.42.5388