In x Al 1 − x N films were heteroepitaxially grown on AlN∕Al2O3 (0001) templates by molecular beam epitaxy. The compositions studied spanned the whole ternary range. The complex dielectric function of the films was investigated by variable angle spectroscopic ellipsometry in the energy range from 0.55to6eV. The energy bandgap bowing parameter was found to strongly depend on composition, monotonically increasing with decreasing InN mole fraction. This behavior is in agreement with theoretical predictions of large charge transfer contributions to bandgap bowing.

A detailed discussion of the optical properties of Al-rich Al 1−x In x N alloy films is presented. The (0001)-oriented layers with In contents between x = 0.143 and x = 0.242 were grown by metal-organic vapor phase epitaxy on thick GaN buffers. Sapphire or Si(111) served as the substrate. High-resolution X-ray diffraction revealed pseudomorphic growth of the nearly lattice-matched alloys; the data analysis yielded the composition as well as the in-plain strain. The complex dielectric function (DF) between 1 and 10 eV was determined from spectroscopic ellipsometry measurements. The sharp onset of the imaginary part of the DF defines the direct absorption edge, while clearly visible features in the high-photon energy range of the DF, attributed to critical points of the band structure, indicate promising crystalline quality of the AlInN layers. It is demonstrated that the experimental data can be well reproduced by an analytical DF model. The extracted characteristic transition energies are used to determine the bowing parameters for all critical points of the band structure. In particular, strain and the high exciton binding energies for the Al-rich alloys are taken into account in order to assess the splitting between the valence band with Γ v 9 symmetry and the Γ c 7 conduction band at the center of the Brillouin zone. Finally, the compositional dependence of the high-frequency dielectric constants is reported.

No abstract

InAlN thin films grown on GaN/Al2O3 (0001) templates by metal-organic vapor phase epitaxy were studied by transmission electron microscopy techniques. V-defects in the form of hexagonal inverted pyramids with {101¯1} sidewalls were observed on the films’ surfaces linked to the termination of threading dislocations. Their origin is explained by the different surface atom mobility of In and Al and the built-in strain relaxation. Indium segregation in the films is influenced by the formation of V-defects, the edges and the apexes of which function as paths of migrating indium atoms diffusing along nanopipes formed at the open-core threading dislocations.

No abstract