  Deuterium diffusion is investigated in nitrogen-doped homoepitaxial ZnO
layers. The samples were grown under slightly Zn-rich growth conditions by
plasma-assisted molecular beam epitaxy on m-plane ZnO substrates and have a
nitrogen content [N] varied up to 5x1018 at.cm-3 as measured by secondary ion
mass spectrometry (SIMS). All were exposed to a radio-frequency deuterium
plasma during 1h at room temperature. Deuterium diffusion is observed in all
epilayers while its penetration depth decreases as the nitrogen concentration
increases. This is a strong evidence of a diffusion mechanism limited by the
trapping of deuterium on a nitrogen-related trap. The SIMS profiles are
analyzed using a two-trap model including a shallow trap, associated with a
fast diffusion, and a deep trap, related to nitrogen. The capture radius of the
nitrogen-related trap is determined to be 20 times smaller than the value
expected for nitrogen-deuterium pairs formed by coulombic attraction between D+
and nitrogen-related acceptors. The (N2)O deep donor is proposed as the deep
trapping site for deuterium and accounts well for the small capture radius and
the observed photoluminescence quenching and recovery after deuteration of the
ZnO:N epilayers. It is also found that this defect is by far the N-related
defect with the highest concentration in the studied samples.
