An evaluation algorithm for the determination of the chemical composition of strained hexagonal epitaxial films is presented. This algorithm is able to separate the influence of strain and composition on the lattice parameters measured by x-ray diffraction. The measurement of symmetric and asymmetric reflections delivers the strained lattice parameters a and c of hexagonal epitaxial films. These lattice parameters are used to calculate the relaxed lattice parameters employing the theory of elasticity. From the relaxed parameters, the chemical composition of the epitaxial film can be determined by Vegard's rule. The algorithm has been applied to InGaN/GaN/Al2O3(00.1) heterostructures.

Recently a quantum size effect was proposed to be responsible for the blue shift of optical absorption edge and photoluminescence peak wavelength as well as for the porous silicon (PS) formation itself. In the debate about the mechanism of light emission from PS a correlation between particle size and luminescence peak position would be a key test of the confinement approach. In this letter X-ray diffraction results of as-etched PS samples will be presented that indicate a decrease of particle size and an increase of stress in conjunction with a blueshift of photoluminescence wavelength and absorption edge.

IrO 2 and Ir thin films have been deposited by dc sputtering in Ar/O 2 -and pure Ar atmospheres, respectively. The microstructural characterization of the films was done by x-ray diffraction and transmission electron microscopy and showed that ͑nano-͒crystalline Ir and IrO 2 films with different textures could be deposited. Stress analyses showed that the stress of the Ir films can be varied from about Ϫ3.5 GPa for a deposition temperature of 100°C to nearly zero stress if deposited at 500°C. However, IrO 2 films generally exhibited a large compressive stress of about Ϫ1.5 GPa, which is nearly independent of substrate temperature, but changed with texture and stoichiometry of the films. Surface and roughness analyses of the cumulatively annealed samples were performed by various analysis methods, and stoichiometry was examined by Rutherford backscattering spectrometry. In situ stress measurements were used to investigate the stress relaxation behavior of the films up to 900°C. We demonstrate that it is generally possible to optimize reactive IrO 2 sputter deposition by a detailed study of plasma and deposition conditions via recording generic curves for the sputtering system used. At optimized conditions these fine grained IrO 2 films exhibit very high thermal phase stability to at least 800°C for several hours and a very low roughness. The aim of these investigations is to optimize stability of IrO 2 films under high temperature conditions for oxygen barrier application in dynamic random access memory and nonvolatile Fe random access memory cells.

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Epitaxial layers of GaN on c-plane sapphire are analyzed by continuous-wave and time-resolved photoluminescence at 4K and by X-ray diffraction. Besides the well-known emissions from hexagonal GaN we observe luminescence bands at 3.279 and 3.15 to 3.21 eV which are identified as the transition of the donor bound exciton and the donor-acceptor pair recombination in cubic GaN, respectively. Measurements of the luminescence decay times are essential for the clarification of the emission processes. Due to the probing depth of about 200 nm in PL we find that the fraction of cubic phase typically decreases with layer thickness. In our best samples, however, we do not detect the cubic phase at all.