Non-Gaussian Concentration Profile of Hydrogen Diffused in the Zinc Oxide Bulk Crystal

R. Jakieła, A. Barcz Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, PL-02688 Warszawa, Poland

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Hydrogen in ZnO is characteristic for its by high mobility and limited solubility; consequently, the classical Gaussian broadening expected for diffusion from a localized source is not observed after post-implantation annealing. In this work, c-axis ZnO single crystals were implanted with 1 MeV H+ (fluence 1×1016 cm-2), annealed in flowing O2 at 300° and 600° for 15-30 min, and their depth profiles were quantified by secondary ion mass spectrometry. The profiles were observed to evolve in a non-Gaussian manner. At 300° the peak narrows and increases, whereas at 600° the near-peak region is depleted. A long, asymmetric tail and a surface-proximal excess are developed, indicating that rapid out-diffusion, trapping, and limited solubility govern the evolution rather than Fickian spreading. The diffusion coefficient D at 600° was extracted directly from the difference between the initial and annealed profiles. A semi-infinite model with an absorbing surface, with no need to assume a Gaussian initial profile, was applied. Reduction in the overall content after 15 and 30 min at 600° yields the value of D=6×10-9 cm2/s. These results provide a consistent framework for extracting diffusion parameters from non-Gaussian profiles in hydrogenated ZnO, highlighting the dominant role of surface exchange, trapping, and low equilibrium solubility in shaping the measured hydrogen distributions.

DOI:10.12693/APhysPolA.148.267 topics: diffusion, hydrogen, ZnO, secondary ion mass spectrometry (SIMS)