By using capacitance-voltage measurements, the diffusion and field-induced drift of H in GaN p/n+ diodes - grown by metal-organic vapor-phase epitaxy - was measured (figure 2). The data were described well by a computational model which simulated all of the important electronic processes as well as the drift, diffusion and trapping of H in the lattice. The experimental data demonstrated that H existed in the positive charge state. They also suggested that the H diffusivity was anisotropic. At about 200 to 310C, the sum of the activation energies for diffusion and binding of H+ to Mg acceptors was determined to be 2.03eV. This was some 0.6eV larger than previous density functional theory estimates of this quantity. First-principles calculations were presented which demonstrated the observed diffusion anisotropy and which suggested possible reasons why previous treatments underestimated the barrier for H diffusive motion.

Drift, Diffusion and Trapping of Hydrogen in p-Type GaN. C.H.Seager, S.M.Myers, A.F.Wright, D.D.Koleske, A.A.Allerman: Journal of Applied Physics, 2002, 92[12], 7246-52

Figure 2

Diffusion of H in GaN