Identification of hydrogen configurations inp-type GaN through first-principles calculations of vibrational frequencies

We present first-principles calculations for stable and metastable geometries of various hydrogen-related configurations in p-type GaN, including isolated interstitial H as well as Mg-H and Be-H complexes. We also calculate the associated vibrational stretching and wagging modes, systematically including anharmonic contributions to the vibrational frequencies; the anharmonicity is large due to the light mass of the hydrogen atom. Based on our investigations of a large number of configurations we derive a correlation between the vibrational frequency of the stretching mode and the bond length in the N-H bond. The results are compared with experimental results; in particular, we address a new configuration for the Mg-H complex that agrees with the geometrical information extracted from polarization-dependent infrared spectroscopy [B. Clerjaud et al., Phys. Rev. B 61, 8328 (2000)].