A Raman study of hydrogen stretching modes in vacancy-hydrogen defects (VHn
, n = 1,2,3,4) is presented. The positions of the vibrational modes are com
pared to recent IR absorption results. The Raman lines exhibit pronounced p
olarization due to the [111] orientation of the silicon-hydrogen bend. Base
d on the defect symmetry derived from the polarization-dependent Raman sign
als and the Raman intensities we assign the Raman lines to the defects VH4:
2234 cm(-1)(A(1) mode), 2205 cm(-1) (T-2 mode); V2H6: 2180 cm(-1) (A(1g),
mode), 2155 cm(-1) (E-g mode). We tentatively attribute the 2120- and 2099-
cm(-1) lines to VH2 and the 2022-cm(-1) line to VH.