SIMS analysis of impurities and nitrogen isotopes in gallium nitride thin films

Gallium nitride thin films were deposited on sapphire or zinc oxide substrates with a molecular beam epitaxial method. Thin films with a Ga14N/Ga15N/Ga14N isotopic heterostructure were also grown. A CAMECA-type secondary ion mass spectrometry (SIMS) was employed to analyze impurities such as substrate elements. Nitrogen isotopes were also analyzed. Some samples were annealed in a nitrogen atmosphere, and the diffusivities of the elements and isotopes were evaluated. Although the crater surface after using Cs+ ions as the primary ion beam became smoother than after using O2+, preferential sputtering was observed. It is concluded that this preferential sputtering causes the isotope distribution to be abnormal. Elements of the substrates diffused into the thin films