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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.

The microscopic structure of interstitial oxygen in germanium and its associated dynamics are studied both experimentally and theoretically. The infrared absorption spectrum is calculated with a dynamical matrix model based on first-principles total-energy calculations describing the potential energy for the nuclear motions. Spectral features and isotope shifts are calculated and compared with available experimental results. From new spectroscopic data on natural and on quasimonoisotopic germanium samples, new isotope shifts have been obtained and compared with the theoretical predictions. The low-energy spectrum is analyzed in terms of a hindered rotor model. A fair understanding of the center is achieved, which is then compared with interstitial oxygen in silicon. The oxygen atom is nontrivially quantum delocalized both in silicon and in germanium, but the physics is shown to be very different: while the Si-O-Si quasimolecule is essentially linear, the Ge-O-Ge structure is puckered. The delocalization in a highly anharmonic potential well of oxygen in silicon is addressed using path-integral Monte Carlo simulations, for comparison with the oxygen rotation in germanium. The understanding achieved with this new information allows us to explain the striking differences between both systems, in both the infrared and the far-infrared spectral regions, and the prediction of the existence of hidden vibrational modes, never directly observed experimentally, but soundly supported by the isotope-shift analysis. ͓S0163-1829͑97͒08631-1͔

Quantitative data are presented on the infrared (IR) absorption of interstitial oxygen in oxygen-rich silicon using Fourier transform spectroscopy. Besides the well-known 515 and 1106 cm-' room temperature IR bands, due to the symmetric and antisymmetric vibrations of the Si20 entity, respectively, three other bands at 1227, 1720, and 1013 cm-' are reported, whose intensities are scaled with those of the 515 and 1106 cm-' bands. The band at 1227 cm -1 has often been confused with an oxygen precipitate band observed at 1225 cm-' in annealed silicon. Evidence is given that the 1227 cm -~ band is related to interstitial oxygen. It is also shown that another band at 1720 cm -1 is a combination of the antisymmetric mode of Si20 with a phonon combination of the silicon lattice. A weak band at 1013 cm-' is reported for the first time, and it is attributed to an overtone of the 515 cm-' mode.

Abstract. It has been suggested that iron in InP is compensated by a donor, related to the 2316 cm −1 local vibrational mode and previously assigned to the fully hydrogenated indium vacancy, V In H 4 . Using AIMPRO, an ab initio local density functional cluster code, we find that V In H 4 acts as a single shallow donor. It has a triplet vibrational mode at around this value, consistent with this assignment. We also analyse the other hydrogenated vacancies V In H n , n = 1, 3, and determine their structure, vibrational modes, and charge states. Substitutional group II impurities also act as acceptors in InP, but can be passivated by hydrogen. We investigate the passivation of beryllium by hydrogen and find that the hydrogen sits at a bond-centred site and is bonded to its phosphorus neighbour. Its calculated vibrational modes are in good agreement with experiment.

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Abstract. The oxygen isotope sMs of the vibrational modes of interslitid oxygen in silicon, obtained *om isotopically enriched silicon samples, are mmpared with the predictions of a calculation based on a bond-centred location of the 0 atom, as is obtained from fint principles. This camparjson canfirms Ihe existence a f a Raman-active mode in which the 0 atom is weakly involved and of a resonance producing a broadening and a small shift of the " 0 asymmetric mode

Infrared absorption lines observed at low temperature in Zn-doped GaAs epilayers passivated with hydrogen and deuterium are ascribed to As-H and AS-D stretching modes where the As atom involved is the first neighbour of the Zn acceptor. This attribution is shown to be consistent with a model for hydrogen passivation of acceptors on gallium sites in GaAs.