Local vibrational modes of carbon in GaP

Carbon is a common impurity, present as an acceptor, in GaP. The fundamental of the local vibrational mode of 12 C in GaP has been identified at 606.2 cm -1 at 20 K and the identification has been confirmed by investigating the isotope shift in 4 C-doped crystals. An earlier tentative identification of a gap mode of As in GaP at 270.0 cm -1 at 20 K has been confirmed.