Vibrational spectroscopy of group-II-acceptor--hydrogen complexes in GaP

Using infrared absorption spectroscopy, we have observed the local vibrational modes (LVM's) of group-II-acceptor--hydrogen complexes in GaP. In addition to the previously observed zinc-hydrogen complexes, we report modes corresponding to beryllium-hydrogen and cadmium-hydrogen complexes. In GaP:Be, we attribute the modes at 2292.2 and 1669.8 cm-1 to phosphorus-hydrogen and phosphorus-deuterium bond-stretching modes of complexes adjacent to the beryllium acceptors. In GaP:Cd, we attribute the modes at 2434.0 and 1768.3 cm-1 to similar complexes adjacent to the cadmium acceptors. The temperature-dependent shifts of the hydrogen LVM's in GaP:Be and GaP:Zn are shown to be proportional to the lattice thermal energy U(T), a consequence of the anharmonic coupling between the LVM's and the lattice phonons