Plasma-assisted molecular beam epitaxy of NiO on GaN(00.1)

The growth of NiO on GaN(00.1) substrates by plasma-assisted molecular beam epitaxy under oxygen-rich conditions was investigated at growth temperatures between 100 ° C and 850 ° C. Epitaxial growth of NiO(111) with two rotational domains, with epitaxial relation NiO ( 1 1 ¯ 0 ) ‖ GaN ( 11.0 ) and NiO ( 10 1 ¯ ) ‖ GaN ( 11.0 ), was observed by X-ray diffraction and confirmed by in situ reflection high-energy electron diffraction as well as transmission electron microscopy (TEM) and electron backscatter diffraction. With respect to the high lattice mismatch of 8.1% and a measured low residual tensile layer strain, growth by lattice matching epitaxy or domain-matching epitaxy is discussed. The morphology measured by atomic force microscopy showed a grainy surface, probably arising from the growth by columnar rotational domains visible in TEM micrographs. The domain sizes measured by AFM and TEM increase with the growth temperature, indicating an increasing surface diffusion length. Growth at 850 ° C, however, involved local decomposition of the GaN substrate that leads to an interfacial β - Ga 2 O 3 ( 2 ¯ 01 ) layer and a high NiO surface roughness. Raman measurements of the quasiforbidden one-phonon peak indicate increasing layer quality (decreasing defect density) with increasing growth temperature.