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Large Sc-substituted barium hexaferrite crystals were grown by submerged-seeded solution growth (SSSG) and top-seeded solution growth (TSSG) techniques using various seed orientations. The influence of the seed position and seed orientation on the defect formation was studied in detail. Growth defects like inclusions, growth striations, growth sector boundaries, and growth-induced dislocations have been observed at cleaved and polished crystal surfaces by DIC microscopy after selective wet-etching. X-ray topography studies show these defects in more detail. It was found that the seeding process results in the formation of inclusions, which are nucleation centres of growth-induced dislocations. The application of small seed crystals with [2 −1 −1 0] and [0 1 −1 0] seed orientation enables the dislocations, generated by the inclusion, to “grow out” at the side faces of the bulk crystal.

Epitaxial thin films of CuIn1-xGaxS2 (0 ≤ x ≤ 1) were grown on single-crystalline (111)cub-oriented silicon substrates by means of molecular beam epitaxy from elemental sources. Employing reflection high energy electron diffraction and Rutherford backscattering spectroscopy the twinning characteristics and the composition of the films were determined, respectively. X-ray diffraction measurements in transmission geometry were performed to determine the lattice mismatch to the substrate. The degree of twinning of the epitaxial films shows a highly non-linear dependence on their gallium content x. The transition point between high twinning regime (low gallium content) and low twinning regime (high gallium content) is at xt = 0.74. The twinning characteristics are discussed and compared to lattice mismatch and metastable ordering types. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thin epitaxial and polycrystalline CuInS2 (CIS) films were grown on single crystalline Si(111) and Mo-coated Si substrates, respectively, by means of molecular beam epitaxy from elemental sources. Photoluminescence (PL) measurements were performed to investigate the optical properties of both, epitaxial and polycrystalline CIS films. Epitaxial CIS samples show defect related transitions only and the PL spectra are dominated by broad luminescence peaks of deep levels, while excitonic transitions are completely absent. This contrasts sharply with the PL of the polycrystalline films, which is dominated by excitonic luminescence. Contributions due to shallow defects are observed with a small intensity only. However, luminescence peaks of defects with electronic levels deep in the band gap are not present at all. This includes the broad PL lines around 1.2 or 1.3 eV which are typical for polycrystalline CIS solar-cell material. X-ray diffraction and selected area electron diffraction measurements were employed in order to study the crystal structure. The epitaxial CIS films show a coexistence of the metastable CuAu-type (CA) ordering with the ground-state chalcopyrite (CH) structure, while the polycrystalline layers crystallize exclusively in the ground-state CH ordering. Hence, the coexistence of the metastable CA ordering and the ground-state CH structure in the epitaxial films is accompanied by a high density of electrically active intrinsic defects with levels deep in the band gap.

As a precursor material for electrooptical applications in the integrated optics, nominal pure as well as Zn-doped stoichiometric LiNbO 3 thin films of a few μm thickness were grown by liquid phase epitaxy on congruent LiNbO 3 substrates. The crystalline perfection and lattice parameters of the epitaxially grown films were investigated by means of high-resolution X-ray diffraction methods. The symmetric 0/20-diffractograms show a lattice parameter increase perpendicular to the sample surface (Δd/d) ⊥ up to 10 -3 with increasing Zn content. X-ray diffraction reciprocal space measurements taken up with asymmetric reflections are well suited to determine the in-plane lattice parameters of the grown films. Despite different Zn contents, the Zn: LiNbO 3 thin films reveal a distinctly pseudomorphous growth. Using the generalized Hooke's law in matrix way of writing and taking the measured values into account, the relaxed lattice parameters of the grown films as well as the in-plane strain and tension components have been numerically calculated.

Ge nanocrystals were produced in 4H–SiC by implantation of 250 keV Ge+ ions with a dose of 1×1016 cm−2 and subsequent rapid thermal annealing at 1400–1600 °C. Radiation damage and Ge distribution after implantation and annealing were analyzed by Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy methods, and x-ray diffraction. After ion implantation a significant amount of Ge is incorporated into the SiC lattice and Ge nanocrystallites were not found. Thermal annealing leads to a local Ge redistribution and both Ge-rich and Ge nanocrystals are detected after annealing. The size of the nanocrystals varies between 2 and 10 nm.

Different sputtering methods, viz. rf-diode, rf-magnetron, and dc-magnetron sputtering, have been used to increase the sensitivity of Co/Cu/Co/FeMn top spin valve systems by more than a factor of 2. This improvement is due to an enhanced magnetoresistive effect ΔR/R and a reduced anisotropy field Hk for the best sample. In the present paper the transport and magnetic properties are discussed in the context of microstructure and interfacial quality of the multilayers evaluated by comprehensive transmission electron microscopy and x-ray reflectometry investigations. The sample with the highest sensitivity (dc-magnetron sputtered) shows less structural defects and locally smoother interfaces than the other samples. Additionally it is shown that the ferromagnetic interlayer exchange field is not affected by the applied sputtering methods and can be well understood in terms of orange peel coupling.

The lattice parameters of 3C-SiC thin films epitaxially grown on 6H-SiC(0001) substrate crystals have been precisely determined by using high resolution x-ray diffraction methods. Reciprocal space maps recorded around symmetrical and asymmetrical x-ray reflections revealed a pseudomorphic growth of the thin film in relation to the substrate lattice, whereas perpendicular to the surface the interplanar spacing of the lattice planes differ slightly ∆d/d = 8.7⋅10. This implicates inherent thin film strain (e) and stress (σ ) components. The in-plane components are found to be ei = 4.8⋅10 and σi = 2.26⋅10 N/m, whereas perpendicular to the surface the thin film strain component is found to be e^ = 2.8⋅10. Introduction Silicon Carbide (SiC) occurs in many polytypes which differ in their periodic stacking sequences of hexagonal and cubic Si-C bilayers. The SiC lattice parameters differ slightly from polytype to polytype [1]. Using x-ray diffraction methods the lattice parameters of 4Hand 6H-SiC single crystal wafers [2] have been determined precisely (Table 1). Unfortunately, large 3C-SiC single crystals are not available. However, 3C-SiC thin films can be easily grown and used to derive the lattice parameters of compact 3C-SiC crystals if one takes the inherent stress, induced by the thin film growth, into account. The 3C-SiC thin films (thickness ≈ 1.2 μm) were grown by solid-source molecular beam epitaxy on (0001)-oriented on-axis 6H-SiC crystal wafers at deposition temperatures between 780°C to 950°C and with growth rates between 30 nm/h to 120 nm/h [3]. High resolution x-ray diffraction of 3C-SiC thin films Although the lattice parameters of the different SiC polytypes differ only slightly, the x-ray diffraction pattern showed, close to each other but well separated, so-called family reflections of the 3C-SiC thin film and 6H-SiC substrate. Using the well known 6H-SiC bulk crystal values (Table 1) as a reference, we could determine the lattice parameters of the 3C-SiC thin films with a corresponding accuracy of 10 for Da/a and 10 for Dc/c. Reciprocal space maps recorded around symmetrical and asymmetrical x-ray reflections (Fig. 1) revealed a pseudomorphous growth of the 3C-SiC thin films in relation to the substrate lattice (Fig. 2). There is no difference between the lateral interplanar spacing of the lattice planes, but perpendicular to the surface their interplanar spacing differ by ∆d/d = 8.7⋅10. The growth direction of the 3C-SiC thin film was found to be [111] with respect to the surface normal. Silicon Carbide and Related Materials (2001). 319-322 319

The results of using molecular-beam epitaxy for growing piezoelectric AlN films on Si (111) substrates suitable for device applications are reported. The technological conditions for growth of stoichiometric AlN by controlling the surface reconstruction occurring under various thermodynamic conditions on the growth surface are determined. The films of the hexagonal polytype of AlN possess high crystalline perfection and an atomically smooth epitaxial surface. The mechanism for relaxation of the AlN crystal lattice over a distance of one monolayer from the heterojunction is found. It is demonstrated that the AlN film is piezoelectric. Investigations of the temporal characteristics of a SAW attest to a low level of scattering of the wave during propagation. The electromechanical coupling constant is measured in interdigital transducer geometry (λ=16 mm) and is found to be 0.07 % at a frequency f=286 MHz, in good agreement with the theoretical value for a 1.04-µm-thick AlN film.

For the deposition of epitaxial YBa 2 Cu 3 O 7− δ (YBCO) on silicon substrate it is necessary to deposit buffer layers. We use sputtered Y-stabilized ZrO 2 (YSZ) and CeO 2 double layers. Use of sputtering for the deposition of the buffer layers avoids some disadvantages of the pulsed laser deposition, like the effect of droplets, to improve the multilayer technology on silicon with respect to their homogeneity and larger area. The YBCO is ex situ deposited by pulsed laser deposition. RBS and XRD investigations and electrical measurements were applied for the characterization of the single and multilayer films. The correlation between the characterized properties and the used deposition process were analysed. We demonstrate the high quality of the sputtered buffer layer and the applicability of a combined film deposition for YBCO devices on silicon substrates.

Epitaxial growth of SiC on α-SiC(0001) has been performed by means of solid-source molecular beam epitaxy (MBE). Low temperature (T 1200°C, with a step decrease of supersaturation, a step-flow growth mode and for the first time nucleation of both 4H- and 6H-SiC under C-rich conditions was obtained. Based on these results we have demonstrated the growth of a double-heterostructure by firstly growing a 3C-SiC film on 4H-SiC(0001) at low temperature and a subsequent growth of 4H-SiC at low supersaturation on a C-stabilized surface on top of this film. Moreover, we also propose a new model to explain quantitatively the occurrence of different growth features and polytypes under certain growth conditions.

3C–SiC thin films have been investigated by means of high resolution X-ray diffraction techniques ( ω /2Θ-scan, ω- scan) and X-ray topography. The SiC films were grown in a solid source molecular beam epitaxy (MBE) system on 6H–SiC substrate crystals. We investigate the lattice mismatch parallel and perpendicular to the [0001]-direction using the so-called reciprocal space mapping technique. When 3C–SiC films were grown on 6H–SiC substrates, double position boundaries (stacking sequence ACB instead of ABC) were frequently observed. For the visualization of this effect high resolution X-ray topographic measurements are investigated at 3C–SiC layers on 6H–SiC substrates. We find, that the domains of different stacking sequences are equally distributed in the 3C–SiC epilayer. This domains attain a size up to approximately 200×200 μm 2 .

The atomic structure of the two SiC polytypes, 4H– and 6H–SiC, differs by the stacking sequences of the Si–C bilayers in the [0001] direction. Conforming with the space group symmetry, the atoms are in principle allowed to move freely in [0001]-direction. The bonding tetrahedra are pressed or stretched (atomic relaxations). These atomic relaxations are determined by means of high-precision X-ray diffraction measurements and ab initio calculations. The calculations were performed in the framework of pseudopotential-density-functional theory in the local density approximation. For the experimental determination of these atomic relaxations an analysis ‘quasiforbidden’ reflections is possible. A comparison of the measured data with those for calculated geometries is given. We find a good agreement between the calculated and the experimental data.

Epitaxial aluminum nitride AlN(0001) thin films have been grown by plasma-assisted molecular beam epitaxy (PA-MBE) on Si(111). The influence of the composition of the nitrogen plasma on the crystal quality, as judged by X-ray diffractometry (XRD) and atomic force microscopy (AFM), has been investigated. Under an Al/N vapor phase ratio close to unity atomically smooth AIN films have been grown at 850°C substrate temperature with maximum growth rates of 2.5 nm min - 1 . A √3 × √3 and a more Al-rich 2 × 6-surface reconstruction have been observed. Transmission electron microscopy (TEM) investigations show that these films are homogeneous 2H-AIN single crystals. Their defect structure consists of threading dislocations mostly. The hetero-interface is abrupt and flat. Processed high-resolution (HR) TEM images demonstrate a 4×d Si(T10) to 5 × d AlN(2110) coincidence between substrate and epilayer. The XRD FWHM of the (0002)-diffraction peak of 0.5 μm AIN is 0.06° in the ω/2 scan and 0.32° in the ω scan. Phonon modes of AIN have been detected by Raman and infra-red spectroscopy.

We relate the information about interfacial roughness in multilayers obtained by X-ray reflectometry in the low angle regime to what can be determined from cross-section images taken in a transmission electron microscope (TEM). The interfacial root mean square (rms) roughness for each individual layer can be derived from X-ray reflectometry in specular geometry in Co/Cu multilayer systems. The results are both qualitatively and quantitatively in agreement with results obtained by evaluating cross-section TEM images. Utilising non-specular scans in X-ray reflectometry gives additional details about the growth structure. In Co 1− x Zr x /Cu multilayers we suggest to correlate the Hurst parameter to the grain structure determined by cross-sectional TEM.

The atomic structures of the hexagonal $6H$ and $4H$ polytypes of SiC are determined by means of high-precision x-ray-diffraction measurements and first-principles calculations. The cell-internal relaxations which conform with the space-group symmetry are fully taken into account. Since the tetrahedra are distorted along the [0001] direction, an analysis of ``quasiforbidden'' reflections is possible. The measured and calculated data are compared and discussed in detail especially for $6H$-SiC. We find an almost perfect agreement for the ratio $c/a$ of the lattice constants. A comparison of the measured structure factors with those for calculated geometries is given. The atomic relaxations within the unit cell are derived.

Thin polycrystalline SiC films grown on Si(111) at 830 degrees C using solid state evaporation were characterized by X-ray diffraction, transmission electron microscopy and atomic force microscopy. The thin-film crystallites have a preferred growth orientation azimuthal and nearly perpendicular to the substrate surface. The orientation distribution function was characterized to be Gaussian with full width at half maximum of 2.5 degrees . The size of crystallites normal to the surface (the length of columns) is of the order of the thin film thickness, whilst the size parallel to the surface is in the range 20-70 nm.

We demonstrate the direct heteroepitaxial growth of the quaternary semiconductor CuIn(1−x)GaxS2 on Si(111) substrates by means of molecular-beam epitaxy. Using Rutherford backscattering, x-ray diffraction, transmission electron microscopy, and photoreflectance, samples of various Ga contents, x, were characterized in detail. Epitaxial growth was achieved in the whole compositional range and perfect lattice match between the epitaxial layer and substrate was obtained for x≈0.5. The epitaxial layers show the coexistence of bulk chalcopyrite and metastable CuAu-type cation ordering. Photoreflectance data reveal a linear increase of the fundamental band gap with increasing Ga content.

We demonstrate the direct heteroepitaxial growth of the ternary semiconductor CuGaS2 on Si(111) substrates by means of molecular beam epitaxy. X-ray diffraction data prove the epitaxial growth of the CuGaS2 films in the highly ordered chalcopyrite structure. Using photoluminescence, we are able to detect strong excitonic emissions up to room temperature, while photocurrent spectra reveal the A, B, and C valence-to-conduction-band transitions as they are typical for the tetragonal chalcopyrite structure.

The controlled growth of SiC heteropolytypic structures consisting of hexagonal (α-) and cubic (3C-) polytypes has been performed by solid-source molecular beam epitaxy. On on-axis substrates, 4H/3C/4H-SiC(0001) and 6H/3C/6H-SiC(0001) structures were obtained by first growing some nanometers thick 3C-SiC layer at lower temperatures (1550 K) and Si-rich conditions, and subsequent growth of α-SiC on top of the 3C-SiC layer at higher temperatures (1600 K) under more C-rich conditions. On off-axis substrates, multi-heterostructures consisting of 4H/3C- or 6H/3C-stacking sequences were also obtained by first nucleating selectively wire-like 3C-SiC nuclei on the terraces of well-prepared off-axis α-SiC(0001) substrates at low T (< 1500 K). Next, SiC was grown further in a step-flow growth mode at higher T and Si-rich condition. After the growth many wire-like regions consisting of 3C-SiC were found within the hexagonal SiC layer material matrix indicating a simultaneous step-flow growth of both the cubic and the hexagonal SiC material.

The growth and structure of Si- and Ge-nanocrystals was investigated using high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM). AFM-images were used to determine the lateral and vertical dimensions of the nanocrystal. HRXRD measurements show clearly that Si- and Ge-nanocrystals grow on 6 H –SiC(0001) preferentially in two different orientations — 〈111〉 and 〈110〉 — with respect to the surface normal. The growth of Ge-nanocrystals on Si-rich 6 H –SiC(0001) surfaces leads to the formation of Si/Ge-alloy nanocrystals. Both types of nanocrystals grow coherently with respect to the substrate. Hence, due to the respective lattice mismatch, the degree of coherence was found to be much better for Si-nanocrystals.

The epitaxial growth of crystalline wurtzite AlN thin films on (001) Si substrates by plasma-assisted molecular-beam epitaxy is reported. The nucleation and the growth dynamics have been studied in situ by reflection high-energy electron diffraction. Cross-sectional transmission electron microscopy and x-ray diffraction investigations revealed a two-domain film structure (AlN1 and AlN2) with a 30° rotation between neighboring domain orientations and an epitaxial orientation relationship of [0001]AlN∥[001]Si and 〈0110〉AlN1∥〈2110〉AlN2∥[110]Si. A model for the nucleation and growth mechanism of 2H–AlN layers on Si(001) is proposed.

Precise measurements of lattice parameter and photoluminescence were performed across InP-substrates and InP/InGaAsP-DHS. They show a lattice dilation in a region with enriched free carrier concentration if strongn-type doped InP-substrates of faceted 〈111〉-grown LEC-crystals were used. Strain gradients and mismatch problems have to take into consideration.

Combining localised and global structural information we suggest that differences in the magnetoresistive effect in the first maximum of antiferromagnetic coupling in Co/Cu multilayers can be attributed to the number of magnetic shortcuts localised at grain boundaries. In particular evidence is given that the increased rms-roughness in samples without buffer as compared to samples grown on a Fe buffer can be attributed to a break off of the multilayer structure in adjacent grains.

Epitaxial thin films of $\mathrm{Cu}{\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}{\mathrm{S}}_{2}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}1)$ were grown on single-crystalline silicon substrates of (111) orientation by means of molecular-beam epitaxy from elemental sources. Employing x-ray diffraction in transmission and reflection geometries, as well as Rutherford backscattering spectroscopy, the lattice parameters and compositions of these films were determined, respectively. A linear dependence of the lattice constants $a$ and $c$ on the gallium content $x$ was found. Best lattice match with the cubic silicon substrate was observed for $x=0.56$. Furthermore, the coexistence of the metastable CuAu-type ordering with the ground-state chalcopyrite structure was found to depend on the gallium content. This coexistence of the stable ground-state structure with a metastable ordering is accompanied by a nonlinear dependence of the tetragonal distortion on the gallium content of the thin films.

Using molecular beams, polycrystalline CuInS2 (CIS) films were deposited on Mo-covered Si substrates. In order to investigate the influence of growth-induced strain on the optical and structural properties, detailed photoluminescence, photoreflectance and x-ray diffraction (XRD) measurements were performed. The transition energy of the free A-exciton (FXA) transition decreases with (i) decreasing thickness of the CIS layer at a constant thickness of the Mo buffer layer and (ii) increasing thickness of the Mo buffer layer at a constant CIS layer thickness. This appreciable redshift of FXA is accompanied by an increase of the energetic splittings between FXA, FXB, and FXC. When we compare theoretically predicted valence band splittings as a function of the crystal field—obtained from the calculated relative valence band energies—to our experimental values, a completely coherent picture is obtained. We also derived the structure of the conduction band as a function of crystal field, based on the theoreticall...

Thin layers of the ternary chalcopyrite semiconductor CuInS2 grown epitaxially on Si(001) substrates were investigated with respect to the existing phases and their lattice parameters by means of x-ray diffraction at the European Synchrotron Radiation Facility in Grenoble (France). The predominant parts of the samples exhibit the metastable CuAu-type ordering. The smaller volume fractions of the samples showing the ground-state chalcopyrite ordering are distorted in order to accommodate themselves to the tetragonal CuAu-type structure. It is suggested that this finding is a consequence of the growth mode of CuInS2 thin films.