Vibrational modes of carbon doped InP have been investigated by Raman scattering and cluster‐Bethe‐lattice calculations. In contrast to other carbon doped III–V semiconductors, the InP samples grown by metalorganic molecular beam epitaxy (MOMBE) shown‐type conductivity. Raman spectra from such samples reveal a vibrational mode at 220 cm−1. The frequency of this mode lies in the gap between the acoustic and optical branches of the phonon dispersion (gap mode). Cluster‐Bethe‐lattice calculations predict such a gap mode only for the carbon donor on the In site and not for the carbon acceptor on the P site. ©1995 American Institute of Physics.