Two infrared local vibrational mode (LVM) absorption lines occurring at 715 and 845 cm−1 shift to 679 and 802 cm−1 in gallium arsenide doped with 18O, proving that the lines arise from the vibrations of oxygen impurities. The 715 cm−1 line exhibits a triplet 69,71Ga isotope fine structure consistent with that expected from a quasi-substitional VAs-O center. The 845 cm−1 line appears as a closely spaced doublet expected for a bonded interstitial oxygen atom.

We have measured and analysed the Raman-scattering and far-infrared spectra from unoriented n-and p-type Hg, -,Cd,Te with x 0.21. Measurements were made in the 80-180 cm" frequency region at temperatures of 10 and 80 K. Comparison of the n-and p-type spectra leads to the conclusion that the electronic contribution to the Raman spectra is small. In particular, the data show that the 135cm" feature originates in lattice effects and may be related to the Te-3Hg-Cd combination as previously suggested. The weak but distinct fine structure present in the CdTe-like reststrahlen band at -153 cm" is tentatively assigned to be a result of localised oscillations of Cd ions in the alloy lattice. A study of the spectral changes between 10 and 80 K clearly indicates a softening of the HgTe-like TO phonon

Far-infrared Fourier transform spectroscopy has been applied to study residual shallow acceptors in as-grown semi-insulating GaAs. Secondary optical excitation into the EL2 absorption band has been used to create a nonequilibrium hole population to neutralize the acceptors. Optically induced absorption spectra from carbon and zinc acceptors have been observed. The dependence of these spectra on the secondary illumination is studied. A comparison is made with electronic Raman spectra recorded from the same samples.

The incorporation of Si in ion-implanted and thermally annealed GaAs has been studied by local vibrational mode spectroscopy. Raman scattering and Fourier transform IR absorption have been used to analyze the Si site distribution both in the near surface region and averaged over the whole implanted layer, respectively. The samples implanted with doses of 5×1014 –1016 cm−2 were annealed with various techniques using different capping layers. The Si site distribution is found to depend strongly on the details of the annealing. In particular, capping with SiO2 leads to the formation of the so-called Si-X defect complex in addition to the incorporation of Si on both lattice sites and the formation of nearest-neighbor Si pairs.

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