To clarify the formation mechanism of H-2* in Si; we studied the dependence
of the concentration of HT on the electron-irradiation dose: in hydrogenat
ed Si crystals. Specimens were prepared from high-purity, B-doped and C-dop
ed Si crystals. They were doped with H by annealing in H-2 gas at 1300 degr
ees C followed by quenching. They were irradiated by 3 MV electrons at room
temperature (RT). We measured their optical absorption spectra at 7 K by a
n fourier-transform infrared absorption spectroscopy (FT-IR) spectrometer.
The intensity of the 1838 cm(-1) peak which is due to H-2* was found to be
the weakest in C-doped Si, medium in B-doped Si and the strongest in high-p
urity Si. This tendency correlates with that of the intensity of the 2122 c
m(-1) peak which is due to a complex of a vacancy and two H atoms. The. int
ensity of the 1838 cm(-1) peak linearly depends on the electron dose at low
doses. These results suggest two mechanisms for the formation of H-2* from
H-2, namely, a combination of a vacancy and an H-2 or a combination of a F
renkel pair and an H-2.