The structure of the H-related complexes in p-type InP and in liquid encapsulated Czochralski semiinsulating InP:Fe has been studied from the vibrational absorption of their PH stretching modes. The acceptor complexes are produced by plasma hydrogenation so that PD modes have been investigated also. The study has first been performed at 6 K on the fundamentals and on the most intense of the first overtones. The trends in the frequencies and widths of the PH modes of the H-acceptor complexes for Be, Zn, and Cd acceptors are discussed and explained qualitatively. In InP:Fe, the PH intrinsic modes are sharper than those of the acceptor complexes indicating a weaker interaction with the environment. This study has been followed by the measurement of the temperature dependence of the frequencies and of the linewidths for increasing temperatures. The frequency shifts and the broadenings of the lines are interpreted by the temperature-dependent random dephasing of the vibration of the high-frequency oscillators in the excited state. The analysis shows that the PH mode in the acceptor complexes couples to TA phonons of the InP lattice while the one in the complexes involving a vacancy couples to a two TA phonon combination. The anharmonicity of the P-H bonds is comparable to the one in phosphine. A comparison of the anharmonicity parameters derived from the overtone measurements with those derived from the hydrogen isotope effects gives evidence of the interaction between the H atom and the lattice. The amplitude of vibration of the D atom is smaller than that of the H atom and this explains why the interaction of the D atom with the lattice is smaller. This is the reason why the width of the PD modes is smaller than that of the corresponding PH modes. The splitting of some of the PH lines in samples subjected to a uniaxial stress has been studied. The splitting of the PH;Zn mode is in full agreement with a P-H bond along a (111)axis. The same (111)orientation of the P-H bond is also found from the splitting of a line attributed to an In vacancy "decorated" by a H atom ( VI"(PH)). The splitting of the strongest line in InP:Fe leads to its attribution to a PH mode in a cubic center containing four H atoms ( V&"(PH)4). The presence of this center seems to account for most of the hydrogen present in InP:Fe. Upon annealing of the InP:Fe samples, V&"(PH)4 is a source of atomic hydrogen that can be trapped by other defects and it can leave partially hydrogenated In vacancies.

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