Hydrogen configurations, formation energies, and migration barriers in GaN

Hydrogen configurations, formation energies, and migration barriers in GaN have been obtained from density-functional theory (DFT) calculations employing the generalized-gradient approximation (GGA) for exchange and correlation. The H configurations and formation energies are similar to previous DFT results obtained using the local-density approximation (LDA) for exchange and correlation with the most notable differences being higher formation energies for H0 (0.2 eV) and H2 (0.1 eV) in the GGA calculations and a preference for H+ at a bond-centered site. GGA H migration barriers differ from LDA values with the largest differences being 0.4 eV higher GGA H+ migration barriers. Refined measurements of field-induced H+ drift in GaN p/n+ diodes have also been performed. Modeling of these results indicates that the sum of the H+ diffusion activation energy and the H+ binding energy to ionized Mg acceptors is 1.76 eV. The corresponding GGA result (1.6 eV) is in good agreement with the measured value.