Drift, diffusion, and trapping of hydrogen in p -type GaN

Using capacitance–voltage measurements we have measured both the diffusion and the field-induced drift of H in GaN p/n+ diodes grown by metalorganic vapor phase epitaxy. Our data are well described by a computational model which simulates all of the important electronic processes as well as the drift, diffusion, and trapping of hydrogen in the GaN lattice. The experimental data demonstrate that H exists in the positive charge state; they also suggest that hydrogen diffusivity is anisotropic in this hexagonal material. In the temperature range from ∼200 to 310 °C we have determined that the sum of the activation energies for diffusion and binding of H+ to magnesium acceptors is 2.03 eV. This is ∼0.6 eV larger than previous density functional theory estimates of this quantity. We present first-principles calculations which demonstrate the observed diffusion anisotropy and which suggest possible reasons why previous treatments underestimate the barrier for hydrogen diffusive motion.