Synchrotron tomography and AlN-GaN growth on silicon

Sub-μm synchrotron tomography of multiphase metals using Kirkpatrick-Baez optics

G Requena et al

High resolution 3D imaging of heterogeneous metals is performed by high energy magnified synchrotron tomography using Kirkpatrick-Baez focusing optics achieving voxel sizes of (50-60 nm)3. Absorption and phase contrast are exploited applying holotomographic reconstructions. Microstructural features as small as not, vert, similar 180 nm are detected in ternary eutectic Al-Mg2Si-Si, SiC particle reinforced AlCu4, near β Ti-10V-2Fe-3Al, and in TiB reinforced α+β Ti-6Al-4V. The phase retrieval procedure yields enough contrast to segment the individual phases and analyze their shapes and 3D architecture.

Sequential growths of AlN and GaN layers on as-polished 6H–SiC(0001) substrates

Z J Reitmeier et al

Microstructures of surfaces and defects generated during initial and subsequent growths via metalorganic vapor-phase epitaxy of AlN(0001) films on 6H–SiC(0001) substrates and GaN(0001) films on AlN/SiC(0001) substrates have been investigated using atomic force microscopy and cross-sectional and plan-view transmission electron microscopy. Scratches present on the SiC surfaces did not appear to bias the nucleation of AlN. The lateral growth rate of AlN was greater than the vertical growth rate, leading to almost planar layers at 15 and 100 nm thicknesses. Partially coalesced islands were observed after nominally not, vert, similar15 nm of growth. Increasing the thickness to 100 nm resulted in complete island coalescence, formation of undulating films from the polishing scratches in the SiC substrate, a surface microstructure containing steps, terraces and small pits, and a reduced dislocation density relative to the 15 nm layers. The AlN/SiC interfaces contained steps and complex dislocation networks. GaN islands nucleated and grew on the AlN films. Complete coalescence of these islands occurred at thicknesses less than 100 nm. Dislocation density in the GaN films was reduced by increasing the thickness of either the AlN and or the GaN. Arguments are developed to account for these observations.