The III-nitrides include the semiconductors AlN, GaN and InN, which have band gaps spanning the entire UV and visible ranges. Thin films of III-nitrides are used to make UV, violet, blue and green light-emitting diodes and lasers, as well as solar cells, high-electron mobility transistors (HEMTs) and other devices. However, the film growth process gives rise to unusually high strain and high defect densities, which can affect the device performance. X-ray diffraction is a popular, non-destructive technique used to characterize films and device structures, allowing improvements in device efficiencies to be made. It provides information on crystalline lattice parameters (from which strain and composition are determined), misorientation (from which defect types and densities may be deduced), crystallite size and microstrain, wafer bowing, residual stress, alloy ordering, phase separation (if present) along with film thicknesses and superlattice (quantum well) thicknesses, compositions and non-uniformities. These topics are reviewed, along with the basic principles of x-ray diffraction of thin films and areas of special current interest, such as analysis of non-polar, semipolar and cubic III-nitrides. A summary of useful values needed in calculations, including elastic constants and lattice parameters, is also given. Such topics are also likely to be relevant to other highly lattice-mismatched wurtzite-structure materials such as heteroepitaxial ZnO and ZnSe.

https://iopscience.iop.org/article/10.1088/0034-4885/72/3/036502/pdf

X-ray diffraction of III-nitrides

http://w0.rz-berlin.mpg.de/hjfdb/pdf/260e.pdf

Metal deposits on well-ordered oxide films

Instabilities in semiconductor heterostructure growth can be exploited for the self-organized formation of nanostructures, allowing for carrier confinement in all three spatial dimensions. Beside the description of various growth modes, the experimental characterization of structural properties, such as size and shape, chemical composition, and strain distribution is presented. The authors discuss the calculation of strain fields, which play an important role in the formation of such nanostructures and also influence their structural and optoelectronic properties. Several specific materials systems are surveyed together with important applications.

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Structural properties of self-organized semiconductor nanostructures

Probing surface and interface morphology with Grazing Incidence Small Angle X-Ray Scattering

Introduction to Mathematical Statistics. By R.V. Hogg and A. T. Craig. Pp. ix, 245. 47s. 1959. (The Macmillan Company, New York)

The term “dissipative structures” which was introduced by Prigogihe [17] describes a broad class of non-equilibrium systems where a constant flow of energy and/or matter leads to structures ordered in space or time, e.g. causes kinetic oscillations or spatial pattern formation. Temporal oscillations and spatial pattern formation are closely related since the same kinetic instabilities which lead to a periodic variation of the system variables in time may also induce a periodic variation in space. Consequently one often observes spatio-temporal structures, but one may also consider the case of a non-equilibrium structure which is only periodic in space. Such structures which rarely have been observed in chemical reaction systems were first discussed by Turing [20] and have been termed accordingly as “Turing structures”.

/pdf/spatial-pattern-formation-in-a-catalytic-surface-reaction-vjhhmei0cw.pdf

Spatial pattern formation in a catalytic surface reaction: The facetting of Pt(110) in CO+O2.

Defect analysis at surfaces with LEED or RHEED have so far been essentially restricted to steps or superstructure domains. Even if there are no superstructures, variations of the scattering factor influence the spot profile. With the now available high-resolution instruments more details of the spot profile may be observed. Therefore it will be discussed how a careful study of the spot profile at different energies may be used to analyze a surface with simultaneous steps and inhomogeneities. It will be shown how the asperity height is obtained without fitting parameters and how inhomogeneities are analyzed with respect to coverage and size distribution.

Electron diffraction at stepped homogeneous and inhomogeneous surfaces

We have determined the atomic structure of the Si(111)-(\ensuremath{\surd}7\ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}7)Co surface using scanning tunneling microscopy and ion scattering. The unit cell contains one surface substitutional cobalt atom centered under a six silicon adatom cluster. High-temperature annealing produces a low density lattice gas of these ringlike clusters, giving rise to an ``impurity stabilized 1\ifmmode\times\else\texttimes\fi{}1'' structure. They occur for several other transition metals, suggesting a stable, universal, silicide related structure.

Ring clusters in transition-metal-silicon surface structures.

The interaction of nitrogen, oxygen, and hydrogen plasmas with spin-coated arrays of colloidal cobalt–platinum particles was investigated with a large variety of microscopic and spectroscopic techniques. It could be demonstrated that the organic ligands of the nanoparticles can be completely removed. Yet, due to the short (∼1.6 nm) interparticle distances within the layers, strong degradation and sintering effects are observed after hydrogen and nitrogen plasma treatments. In the case of oxygen plasma, the shape and size of the individual particles are unaffected and can be preserved, even if a short hydrogen plasma is subsequently applied to reduce the particles back to their metallic state. Nevertheless, the mesoscopic order of the particle arrays is slightly decreased as observed by the breakup of larger ordered areas into smaller domains forming island–trench structures. Probing the surface chemistry of the particles with temperature programmed desorption, a rather complex surface chemistry is found to result from the plasma treatments. The first TPD spectrum after the cleaning process with oxygen and subsequent hydrogen plasmas reveals that the particles are loaded with adsorbed and implanted hydrogen. After removal of this hydrogen, subsequent TPD spectra using CO as a probe molecule, show broad signals between 190 and 360 K pointing to nonmetallic surface properties. While the platinum was found to be completely reduced, XPS measurements reveal a remaining fraction of oxidic cobalt species which are enriched at the surface. Thus, although the structure of the close-packed Co–Pt nanoparticle arrays can be qualitatively preserved during plasma-based ligand removal, the treatment leads to a complex materials system the chemical properties of which are influenced by the particle components, the substrate, and the plasma media.

Structural and Chemical Effects of Plasma Treatment on Close-Packed Colloidal Nanoparticle Layers

The structure and composition of the GaAs(001) surface was studied with high-resolution medium-energy ion scattering, from As-rich to Ga-rich reconstructions. In contrast to commonly accepted models, we find that first and second layers in the surface may contain both Ga and As atoms. The surfaces are more Ga-rich than previously believed, with Ga atoms occupying As sites. Such mixed compositions are explained by consideration of charge neutrality, as well as Coulomb repulsion between surface electrons

Jens Falta

Papers

Spatial pattern formation in a catalytic surface reaction: The facetting of Pt(110) in CO+O2.

Electron diffraction at stepped homogeneous and inhomogeneous surfaces

Ring clusters in transition-metal-silicon surface structures.

Structural and Chemical Effects of Plasma Treatment on Close-Packed Colloidal Nanoparticle Layers

Structure and composition of GaAs(001) surfaces.