Hydrogen molecules in boron-doped crystalline silicon

Boron-doped, float zone silicon has been hydrogenated at 1300 degrees C and then quenched to room temperature. Infrared absorption measurements of the samples in their as-quenched state and following anneals at 160 degrees C reveal the vibrational mode from H-B pairs, together with the line that we have assigned to the vibrational mode of isolated hydrogen molecules (nu(3)HH = 3618 cm(-1)). Annealing leads to irreversible increases in the concentrations of H-B pairs and decreases in the concentration of nu(3HH) centres. The results imply that H-2 molecules diffuse to boron accepters and that there is subsequent dissociation of these molecules with the formation of H-B pairs. The measurements confirm an earlier proposal that 'hidden hydrogen' present in such samples is in the form of isolated molecules.