Hydrogen local vibrational modes

Key words Hydrogen binding energy, hydrogen local vibrational modes, hydrogen concentration, hydrogen density-of-states distribution... 

Nickel, N. H. and Fleischer, K. (2003) Hydrogen local vibrational modes in zinc oxide Physical Review Letters, 90(19). 

In Chapter 8, Stavola and Pearton discuss the local vibrational modes of complexes in Si that contain hydrogen or deuterium. They also show how one can use applied stress and polarized light to determine the symmetry of the defects. In the case of the B-H complex, the bond-center location of H is confirmed by vibrational and other measurements, although there are some remaining questions on the stress dependence of the Raman spectrum. The motion of H in different acceptor-H complexes is discussed for the Be-H complex, the H can tunnel between bond-center sites, while for B-H the H must overcome a 0.2 eV barrier to move between equivalent sites about the B. In the case of the H-donor complexes, instead of bonding directly to the donor, H is in the antibonding site beyond the Si atom nearest to the donor. The main experimental evidence for this is that nearly the same vibrational frequency is obtained for the different donor atoms. There is also a discussion of the vibrational modes of H tied to crystal defects such as those introduced by implantation. The relationship of the experimental results to recent theoretical studies is discussed throughout. 

Besides the electrically active complexes discussed above, there is indirect evidence for the existence of neutral complexes. In close analogy to the observations in silicon and several III-V materials it appears that hydrogen passivates deep and shallow acceptors. Because of the small concentrations of these neutral centers, all attempts to detect them directly with local vibrational mode (LVM) spectroscopy or electron paramagnetic resonance (EPR) have been unsuccessful. 

Determination of the local vibrational modes (LVM) of the Mg-H complex in GaN provides satisfying confirmation of the significance of hydrogen in GaN and useful information, when compared with theory, on the structure of the complex. At the present time the stretch frequency is in fact the only reliably established physical parameter available from experiment for the Mg-H complex in GaN. 

Local vibrational mode (LVM) spectroscopy is a tool suited to study this problem. The knowledge about LVMs supplies a detailed information about the physical properties of light impurities embedded in ZnO. The frequencies of the LVMs reveal directly the chemical binding of hydrogen with its neighbors due to the dependence on the atomic structure of the hydrogen-related defects. 

In summary, Raman backscattering measurements showed the presence of C-Hx and N-H local vibrational modes in single crystal ZnO. Heating the specimens to temperatures of up to 950 °C caused hydrogen out diffusion. After dehydrogenation the local vibrational modes disappeared indicating that they are related to the presence of H. From H effusion measurements the... 

In the INS of hydrogen on powdered platinum [52] peaks in the difference spectrum were observed at 70 and 150 cm, correlating with peaks in the bulk vibrational spectrum of platinum, and at 400 cm, assigned to a local vibrational mode of hydrogen coupled to platinum. 

Chevallier et al. (1990) summarize hydrogen local mode vibrations that have been observed either in as-grown (Riede et al., 1988 Dischler and... 

FREQUENCIES OF THE HYDROGEN LOCAL MODES OF VIBRATION AT 5 K OBSERVED IN BULK III-V MATERIALS. WHEN OBSERVED, THE CORRELATION WITH A DOPANT IS INDICATED. 

The most commonly accepted model for the hydrogen-acceptor pairs locates H at the BC site (see Fig. 4). This model was originally proposed for the H—B complex on the basis of satisfied bonds to explain the increased resistivity (Pankove et al., 1983), SIMS profiles (Johnson, 1985), and a hydrogen local-mode frequency consistent with a perturbed hydrogen-silicon bond (Pankove et al., 1985 Johnson, 1985 Du et al., 1985). The acceptor deactivation by atomic hydrogen was subsequently observed for Al, Ga, and In acceptors in silicon (Pankove et al., 1984). Hydrogen local-mode vibrations were identified as well for the H—Al and H—Ga complexes (Stavola et al., 1987). The boron vibrational frequency for the H—B pair was first identified by Stutzmann (1987) and Herrero and Stutzmann (1988a). 

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