Stability, diffusivity, and vibrational properties of monatomic and molecular hydrogen in wurtzite GaN

Abstract

The stability and diffusivity of monatomic (H+ and H−) and molecular (H2) hydrogen in wurtzite GaN are studied via first-principles calculations. Stable configurations are identified and the formation energies are studied as a function of the Fermi level. Diffusion barriers in the direction parallel to [0001] (||c) and perpendicular to [0001] (⊥c) are calculated. For H+ the diffusion barriers are slightly higher than in the zinc-blende phase and modestly anisotropic (0.85 eV ⊥c, 0.94 eV ||c). For H− the diffusion barriers are lower than in zinc-blende GaN, with values of 1.99 eV and 2.17 eV for ||c and ⊥c, respectively. The diffusion barriers for H2 are relatively high (2.0 eV for ||c and 2.2 eV for ⊥c), and we propose that diffusion of H2 is more likely to proceed by dissociation followed by diffusion of monatomic H+. The vibrational frequency of the molecule in wurtzite GaN is redshifted from the free molecule; for wurtzite GaN the frequency is 129 cm−1 lower than in free H2. Finally, we find that the H2* complex is only slightly higher in energy than interstitial H2, and we calculate its vibrational frequencies. © 2003 The American Physical Society.