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Coherent In x Al 1−x N (x = 0.15 to x = 0.28) films were grown by metalorganic chemical vapor deposition on GaN templates to investigate if the films obey Vegard’s Law by comparing the film stress-thickness product from wafer curvature before and after In x Al 1−x N deposition. The In composition and film thickness were verified using atom probe tomography and high resolution X-ray diffraction, respectively. Ex-situ curvature measurements were performed to analyze the curvature before and after the In x Al 1−x N deposition. At ∼In 0.18 Al 0.82 N, no change in curvature was observed following InAlN deposition; confirming that films of this composition are latticed matched to GaN, obeying Vegard’s law. The relaxed a 0 - and c 0 - lattice parameters of In x Al 1−x N were experimentally determined and in agreement with lattice parameters predicted by Vegard’s law.

We developed a model for in-situ wafer curvature values of AlInN/GaN distributed Bragg reflectors (DBRs) and determined InN mole fractions in the DBRs with the model. In order to develop the model, we experimentally investigated contributions of substrate temperature ramping and a GaN growth to changes in the in-situ curvature values during the AlInN/GaN DBR growth. We found that an increase of curvature changes at the substrate temperature ramping steps was explained by an increase of the total epitaxial layer thicknesses. Another finding was that strain in the GaN layers at the GaN layer growth steps was almost zero. Finally, we determined the InN mole fractions in the AlInN layers by using the model, showing excellent agreements with the values estimated from ex-situ X-ray diffraction measurements. The model reveals not only the entire in-situ curvature change profile but also the InN mole fraction under the precisely lattice-matched condition of AlInN/GaN DBRs.

The impact of AlN nucleation layers on the strain evolution in a subsequent GaN layer was investigated by in-situ wafer curvature measurement. It is shown that growth temperature and thickness of the AlN nucleation layer strongly influence the built-in strain and crystalline quality of GaN. A two-step AlN growth procedure leads to a decrease of compressive strain as well as the reduction of the total dislocation density (6–9×108 cm−2) in the overgrown GaN layer. TEM analysis reveals different relaxation mechanisms of GaN in v-pits and on flat surfaces of AlN. With a two-step AlN nucleation layer a low wafer bow can be achieved together with a low dislocation density.

The stress evolution of Si-doped AlxGa1−xN epilayers with x ranging from 0 to 0.62 was examined using an in situ wafer curvature measurement technique. Transmission electron microscopy was used to assess the effects of Si concentration and composition on defect microstructure. It was found that the density of edge-type threading dislocations (TDs) increased with increasing x, corresponding to the evolution of higher magnitudes of tensile stress, attributed to TD inclination. The results are discussed in the context of proposed inclination mechanisms that feature jog formation as the process leading to TD inclination.

Stress in a thin film on a flexible substrate induces a curvature of the substrate. Usually the substrate is orders of magnitude thicker than the film, leading to small and purely elastic deformation of the substrate. In this case, the Stoney equation yields the stress in the film from the measured curvature of the substrate. The Stoney equation contains thickness of film and substrate and the elastic properties of the substrate. Typically the elastic properties of the substrate are specified by E (Young's modulus), and ν (Poisson's ratio). E and ν provide a valid description for elastically isotropic substrates, e.g. polycrystalline steel strips, as used by Stoney in 1909. Today the Stoney equation is still used for relating substrate curvature to film stress. However, in the majority of thin film stress measurements by means of substrate curvature, Si wafers are used as the substrate. Silicon wafers are cut from single crystals and are thereby elastically anisotropic. In the present paper, a modified form of the Stoney equation, well known for elastic isotropic substrates, is derived for Si(001) and Si(111) wafers, using the elastic stiffness constants of silicon, cij, instead of the orientation averaged values E and ν, which do not have a meaning for elastically anisotropic single crystal materials. Curvature measurements of thin films on Si(001) and Si(111) wafers are presented. The difference in film-stress-induced curvature of Si(001) and Si(111) wafers is discussed. © 2008 Elsevier B.V. All rights reserved.

Aluminum thin films deposited onto oxidized silicon substrates were deformed using the difference in thermal expansion coefficients between the two materials. Stresses in the Al films were measured by the wafer curvature method. The stress-temperature behavior is explained by cross-sectional TEM studies which revealed grain growth and dislocation exhaustion. In order to track down finer dislocation mechanisms, in situ cross-sectional samples were heated from room temperature up to 450°C in a TEM. Dynamic observations demonstrated that the Al/SiO x –Si interface acts as a sink for dislocations and grain boundaries.