Two wafers of one 4H-silicon carbide (4H-SiC) bulk crystal, one cut from a longitudinal position close to the crystal's seed and the other close to the cap, were characterized with synchrotron white-beam X-ray topography (SWXRT) in back-reflection and transmission geometry to investigate the dislocation formation and propagation during growth. For the first time, full wafer mappings were recorded in 00012 back-reflection geometry with a CCD camera system, providing an overview of the dislocation arrangement in terms of dislocation type, density and homogeneous distribution. Furthermore, by having similar resolution to conventional SWXRT photographic film, the method enables identification of individual dislocations, even single threading screw dislocations, which appear as white spots with a diameter in the range of 10 to 30 µm. Both investigated wafers showed a similar dislocation arrangement, suggesting a constant propagation of dislocations during crystal growth. A systematic investigation of crystal lattice strain and tilt at selected wafer areas with different dislocation arrangements was achieved with high-resolution X-ray diffractometry reciprocal-space map (RSM) measurements in the symmetric 0004 reflection. It was shown that the diffracted intensity distribution of the RSM for different dislocation arrangements depends on the locally predominant dislocation type and density. Moreover, the orientation of specific dislocation types along the RSM scanning direction has a strong influence on the local crystal lattice properties.

Abstract The physical vapor transport (PVT) crystal growth process of 4H-SiC wafers is typically accompanied by the occurrence of a large variety of defect types such as screw or edge dislocations, and basal plane dislocations. In particular, screw dislocations may have a strong negative influence on the performance of electronic devices due to the large, distorted or even hollow core of such dislocations. Therefore, analyzing and understanding these types of defects is crucial also for the production of high-quality semiconductor materials. This work uses automated image analysis to provide dislocation information for computing the stresses and strain energy of the wafer. Together with using a genetic algorithm this allows us to predict the dislocation positions, the Burgers vector magnitudes, and the most likely configuration of Burgers vector signs for the dislocations in the wafer. Graphical abstract

In this paper, we investigate, using X-ray Bragg diffraction imaging and defect selective etching, a new type of extended defect that occurs in ammonothermally grown gallium nitride (GaN) single crystals. This hexagonal “honeycomb” shaped defect is composed of bundles of parallel threading edge dislocations located in the corners of the hexagon. The observed size of the honeycomb ranges from 0.05 mm to 2 mm and is clearly correlated with the number of dislocations located in each of the hexagon’s corners: typically ~5 to 200, respectively. These dislocations are either grouped in areas that exhibit “diameters” of 100–250 µm, or they show up as straight long chain alignments of the same size that behave like limited subgrain boundaries. The lattice distortions associated with these hexagonally arranged dislocation bundles are extensively measured on one of these honeycombs using rocking curve imaging, and the ensemble of the results is discussed with the aim of providing clues about the origin of these “honeycombs”.

X-ray diffraction imaging was used to monitor the local strains that developed around individual n-p-n bipolar transistors within fully encapsulated packages under conditions of extremely high forward bias to simulate accelerated ageing. Die warpage associated with the packaging was observed to relax systematically as the polymer became viscous due to the temperature rise associated with the dissipation of heat in the transistor. The direct image size and intensity from the individual transistors were interpreted in terms of a model in which local thermal expansion is treated as a cylindrical inclusion of distorted material, contrast arising principally from lattice tilt. The extension of the thermal strain image along the emitter with increasing power dissipation was ascribed to the effect of current crowding in the emitter region. Weaker large-area contrast associated with the base-collector region was interpreted as arising from the smaller change in effective misorientation at the high X-ray energy of thermal lattice dilation in the base region.

The review on bulk growth of SiC includes a basic overview on the widely used physical vapor transport method for processing of 4H-SiC boules as well as the discussion of three current research topics: (a) Sublimation bulk growth of large area, freestanding cubic SiC, (b) in-situ Visualization of the PVT Process using 2D and 3D X-ray based imaging and (c) prediction of dislocation formation and motion in SiC using a continuum model of dislocation dynamics (CDD).

Screw-type dislocations like micropipes (MP) and threading screw dislocations (TSD) are prohibiting the function or at least diminishing the efficiency of electronic devices based on silicon carbide (SiC). Therefore, it is essential to characterize wafers in an efficient and fast manner. Molten potassium hydroxide (KOH) etching or white-beam X-ray topography (SWXRT) are either destructive or not economically viable for an in-depth characterization of every wafer of one SiC crystal. Birefringence microscopy is being utilized as a fast and non-destructive characterization method. Instead of microscopic setups, commercially available flat-bed scanners equipped with crossed polarizer foils can be used for fast large-area scans. This work investigates the feasibility of such a setup regarding the detection rate of MPs and TSDs. The results of a full-wafer mapping are compared with birefringence microscopy and KOH etching. In the investigated sample clusters of MPs caused by a polytype switch in the beginning of the growth could be identified by both birefringence microscopy and the flat-bed scanner setup, as well as small angle grain boundaries and TED arrays. However, the resolution of the scanner was not sufficient to identify TSDs. Nevertheless the setup proves to be an easy-to-setup and cheap characterization method, able to quickly identify defect clusters in 4H-SiC wafers.

X-ray diffraction imaging (XRDI) (topography) measurements of silicon die warpage within fully packaged commercial quad-flat no-lead devices are described. Using synchrotron radiation, it has been shown that the tilt of the lattice planes in the Analog Devices AD9253 die initially falls, but after 100 °C, it rises again. The twist across the die wafer falls linearly with an increase in temperature. At 200 °C, the tilt varies approximately linearly with position, that is, displacement varies quadratically along the die. The warpage is approximately reversible on cooling, suggesting that it has a simple paraboloidal form prior to encapsulation; the complex tilt and twisting result from the polymer setting process. Feasibility studies are reported, which demonstrate that a divergent beam and quasi-monochromatic radiation from a sealed X-ray tube can be used to perform warpage measurements by XRDI in the laboratory. Existing tools have limitations because of the geometry of the X-ray optics, resulting in applicability only to simple warpage structures. The necessary modifications required for use in situations of complex warpage, for example, in multiple die interconnected packages are specified.

X-ray topography of the [211] Ge crystal grown by the Cz-method shows that dislocations can be confined within the (1̄11) glide plane.

Phase pure Na-??-alumina ceramics are excellent electrolytes for molten-salt and all-solid-state batteries. However, controlled processing of this complex material is required to obtain the desired phase content, as Na??-alumina can accommodate variable amounts of sodium within its conduction slab. On the one hand, addition of dopant ions (e.g. Li+, Mg2+) influences stability and sodium content of Na-??-alumina. On the other hand, ??-aluminas are prone to sodium evaporation, resulting in compositional changes during high-temperature sintering. Here, we show that while sodium evaporation indeed becomes significant at temperatures > 1300 ?C, Na-??-alumina ceramics of constant total composition can be prepared at strongly variable sintering conditions by applying an encapsulation. Nevertheless, our study reveals that the sodium content in the Na??-alumina crystal structure varies with the processing temperature. This is indicated by changes in the c-lattice parameter, which decreases with increasing sintering temperature, corresponding to an increase in sodium content.

Bent crystals can be used to deflect high-energy charged particles for beam extraction and/or beam collimation at accelerator facilities, thanks to the channelling phenomenon. In the present paper, two perfect silicon mono-crystals were bent using two different methods: sandblasting and the application of a carbon fibre composite. In particular, these samples were obtained for the realization of bent crystal prototypes to be used to steer the 7 TeV proton beam of the Large Hadron Collider in the context of the CRYSBEAM project. The two bending methods were selected since they allow a very homogeneous curvature of the crystals to be obtained, which is essential for high channelling efficiency. Moreover, the deformation obtained is self-standing, i.e. there is no need for any external device to keep the samples bent. Self-standing curvature can be useful because the presence of an external bender could be a severe limitation in the collider beam-pipe. The curvature of the samples was measured through high-energy X-ray diffraction at the ID11 beamline of the European Synchrotron Radiation Facility in Grenoble, France. Since the diffraction efficiencies obtained were in good agreement with theoretical expectations, it follows that the manufacturing techniques did not damage the samples, i.e. the crystallographic quality was preserved. Finally, the crystal quality of the sandblasted sample was investigated in detail at the synchrotron source at Karlsruhe Institute of Technology by X-ray white-beam topography. The measurements showed no diffusion of defects from the machined surfaces to the crystal bulk.

White-beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. The voids are visible because of a dynamical diffraction contrast. It is shown that voids occur only in dislocation-free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density. It is further suggested that the voids originate from clustering of vacancies during the growth process. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.

X‐ray topography—a well‐known diffraction imaging method—is widely used for the characterization of extended crystal defects like dislocations. Herein, the progress toward the quantification besides the number and nature of dislocations is given. The diffracted images include additional information about tilt and strain, which can be measured in real‐time, thanks to the improved digital detection systems. This allows not only the fast mapping of huge samples like 450 mm diameter Si wafers, the in situ observation of the dislocation, or crack dynamics at high temperatures, but also the stress analysis in electronic devices in operando. In addition to typical white X‐ray beam methods like stacks of section topographs, the monochromatic diffraction laminography allows a 3D representation of the dislocation arrays. The merits and limitations of X‐ray topography are demonstrated by semiconductor materials as an example.

A germanium crystal of high purity was grown in H 2 with a maximum dislocation density of 3000 cm −2 , which was estimated by white beam x-ray topography. Due to a dynamical diffraction effect, the topographs revealed the existence of vacancy clusters in the form of voids in dislocation-free parts of the crystal. Etch pit density analysis, the standard technique employed for crystalline wafers to determine dislocation density, failed to reliably represent dislocations in dislocation-free parts of the crystal. On the other hand, we were able to identify a different type of etching pattern for a dislocation-free crystal. Microwave photoconductance decay was utilized to determine the charge carrier lifetime, which was found to be up to 500 μs for regions with dislocations, while being only 100 μs for dislocation-free parts of the crystal.

Founded in the year 1970, the German Association of Crystal Growth DGKK (Deutsche Gesellschaft für Kristallwachstum und Kristallzüchtung e. V.) celebrates in 2020 its 50th anniversary. With actually just nearly 400 individual and institutional members, the DGKK is an important part of the crystal growth community in Europe and well connected worldwide. From the very beginning until today the success of the association is based on the interdisciplinarity of the members coming from all fields of natural sciences and engineering and united in the complexity of the single crystal growth and the cutting edge technology needed. Such a widespread collection of interests and topics, all focusing on structural perfection, optimum performance for technical applications, unique physical properties and last not least in the aesthetic and beauty of crystals may be unique. The DGKK combines and promotes all of the fundamental and applied knowledge in crystal growth science and technology. The current special issue in Crystal Research & Technology reflects the large variety of DGKK in all its facets but it cannot show a fully complete picture – this would be far beyond the limits of a journal issue. A couple of articles reflect the rich history of DGKK and crystal growth in Germany, also featuring some of the most active and successful laboratories in Germany. However, it is not only history but also future for crystal growth and epitaxy in a world where electronic, optic, and opto-electronic devices will be of more importance than any time before. Various articles present recent research topics that eventually will enter our daily life in the future. This also demonstrates that DGKK will be required in the next fifty years for all fields of bulk and epitaxial growth both in theory and practice. Finally, we would like to express our gratitude to Prof. W. Neumann, Editor-in-Chief, Dr. P. Dogandzhiyski, Dr. M. Zastrow and Dr. H. Meskine, Editors of the Crystal Research & Technology, for the kind support to publish all the papers as this special print issue. Financial support of the printed issue by the Fraunhofer Institute IISB (Erlangen, Germany), the Korth Kristalle GmbH (Altenholz,Germany), the ChemPur Feinchemikalien und Forschungsbedarf GmbH (Karlsruhe, Germany) and the PVA Crystal Growing Systems GmbH (Wettenberg, Germany) is also greatly acknowledged. Andreas N. Danilewsky is associated professor for crystallography and materials sciences at the Albert-Ludwigs-University Freiburg, Germany. He is doing basic research in the field of bulk single crystal growth of various semiconductors. The focus is on fluid dynamics and growth kinetics also using external fields and microgravity environment. Another research priority is the defect characterization with high resolution X-ray diffraction methods, and especially the development of in-situ and real-time X-ray diffraction imaging combined with 3-dimensional reconstruction methods. Peter J. Wellmann is a professor for electronic materials at the Materials Department 6 of University of Erlangen-Nürnberg (FAU), Germany. His research focuses on modern topics in semiconductor technology, including crystal growth, epitaxy and characterization of various electronic materials for energy saving. It includes: (i) SiC for power electronic and optoelectronic applications (Crystal Growth Lab: Key Enabling Technology (KET) Centre of the European Union on Industrial Services in Crystal Growth of SiC); (ii) CIGSSe, CZTS and chalcogenide perovskites for solar applications; (iii) electrical, spectroscopic and structural characterization techniques. Wolfram Miller works in the section Fundamental Description of the Leibniz-Institut für Kristallzüchtung (IKZ) in Berlin, Germany. His research comprises calculations on macro-micro, and atomistic scale for understanding the growth processes of single crystal and epitaxial growth. Both questions of process engineering and optimization as well as of fundamental details are in the focus of simulations. His current work is on Ge single crystal growth and on Ga2O3. For the latter mainly the epitaxy is considered but also the growth of bulk crystals.

Due to the functional limitations of SiO2 for SOI applications, alternative dielectric materials have been investigated. Alternative SOI materials in this work include, AlN and AlGaN. The dielectrics were deposited using MOCVD, and with the aid of PECVD deposited SiO2, and the SiO2 was directly bonded to a handle Si wafer. Tensile tests were performed on the samples to examine the fracture behavior and maximum tensile stresses, with results being comparable to a traditional SOI. Characterization was undertaken using TEM to understand the microstructural and interfacial properties of alternative SOI. High crystal quality Al(Ga)N was achieved on a Si(111) substrate that generally contained well defined chemical interfaces. Finally, synchrotron X-ray diffraction topography was used to understand the topographical strain profile of the device and handle wafers. Topography results showed different strain network properties between the device and handle wafer. This work has demonstrated preliminary feasibility of using alternative dielectrics for SOI applications.

After the Second World War academic life as education and research had to be re-established as well as industrial production had to be reinstalled in Germany. This happened separately in the eastern and the western part, that is, in the German Democratic Republic (GDR) and in the Federal Republic of Germany (FRG) where both parts have had a very successful development. Here, we will describe only the most important steps because the main focus of the article is on the development of the societies representing crystal growth in GDR (second section) in FRG (third section), and in unified Germany. Despite all the restrictions, several attempts have been made from both sides to overcome this separation at least for certain events. After the wall opened in 1989 the situation was quickly changed. Crystal growers from east and west came together. In the end the colleagues from the east part joined the Deutsche Gesellschaft für Kristallwachstum und Kristallzüchtung (DGKK) which became the family for all German crystal growers. Details will be given in the fourth section of this article. A major player in re-establishing academic life was Max Volmer, who became the president of the German Academy of Science in 1955. In the nineteen twenties he established the fundamentals of phase transitions and nucleation theory together with other researchers. Now, besides the more general tasks he supported the continuation of this research direction. In order to re-establish education, research, and industry one plant of the industrial crystal growth for optical applications has been established in Jena at VEB Carl Zeiss. There, main contributions were provided for the development of the Kyropoulos process of NaCl, KBr, and LiF as well as the Bridgman–Stockbarger method of CaF2 and KRS-5 (Tl(Br,J), for infrared) crystals. The crystals were used for optics and lenses. In Bitterfeld the Verneuil Method was used for the production of gemstones. Since 1957 industrial growth was performed also in Freiberg/Saxony at “VEB Spurenmetalle Freiberg,” SMF. Since the sixties Ge single crystals and later Si crystals (4″ FZ-Si and 6″ Cz Si) were grown for electronic applications. Since 1970 also research on III-V-compounds started and the production followed 1982. Considering fundamental research, pioneering work was done by Will Kleber at the Mineralogisch-Petrographisches Institut of the Humboldt University of Berlin. His investigations on crystallization speed in undercooled melts (1955) became very famous. Another main player in the field of fundamental research was Heinz Bethge at the University of Halle, the location for electron microscopy of the German Academy of Science. In 1954 he succeeded together with O. Schaffer in obtaining the first pictures of evaporated spiral steps at the penetration point of screw dislocations by electron microscopy. Furthermore, Heinz Bethge was one of the founders of the International Organization for Crystal Growth (IOCG) in 1966. He held a personal membership in the council of IOCG until 1983. In 1963 the subcommision “Kristallzüchtung” (crystal growth) within the German Academy of Science was founded. The first president was Will Kleber. Klaus–Thomas Wilke became the secretary. Both are still well known because of their fundamental books on crystallography and crystal growth. On 23rd April 1965 the “Vereinigung für Kristallographie (VfK)” (Association for Crystallography) was founded in East-Berlin as a group within the “Gesellschaft für Geologische Wissenschaften der DDR” (Society for Geological Sciences of GDR). Hermann Neels was the first VFK president which later also initiated the foundation of the working group “Kristallisation” within VfK, quasi as continuation of the former subcommission “Kristallzüchtung.” This was 1971 and in November of that year the first VfK conference on single crystalline materials was held (the framework was “Semiconductor Crystallography”). During the following years this group was first led by Manfred Jurisch (Dresden) and later by Günther Kühn (Leipzig). At that time key crystal growth activities were developed under the explicit support of the VFK presidents Manfred Schenk (Dresden and Berlin), Hans-Joachim Bautsch (Berlin), Peter Paufler (Leipzig, acting after the unification of Germany as the president of the German Association for Crystallography in 2000–2003) and Ursula Steinike (Berlin). VFK conferences on crystallization were organized in the years 1973, 1975, 1978, 1984, and 1989 as well as about 40 round table discussions were arranged. Very important was the organization of winter schools under the guidance of Manfred Jurisch (Dresden). The first one took place in 1977 and from that time on every three years (see Figure 1). About 100 participants attended these schools, which contributed a lot to establish a broad knowledge of the fundamentals and current developments in crystal growth. It should be noted that during these times the access to certain progress and knowledge was very limited because of the severe travel restrictions in GDR. However, there were contacts for instance between the growers of the Technikum für Kristallzüchtung (at the “Zentrum für wissenschaftlichen Gerätebau” of the GDR Academy of Science) and the development department of Wacker Chemitronic as well to those at the Jülich Research Centre. A contact to the colleagues of the East Bloc was generally not a problem but a participation at an international conference outside this bloc was much more complicated. One action of the working group was the organization of seminars about dedicated international conferences. Typically, a small group of people had the permission to travel abroad to an international conference. Afterward, they were invited to those seminars to give detailed reports on the scientific developments presented at the conference. The other initiative was to invite speakers from FRG and other West-European countries to conferences in GDR. For instance, in 1973 D. D. Double from Oxford (GB) gave a talk about the solidification of eutectic systems on the VfK conference. At the conference five years later Siegfried Haussühl (University Köln) spoke about the systematic search for single crystals with strong polarities. He was the first speaker of DGKK at such a conference. Worth mentioning at this point are the summer schools for crystal growth of the “Council for Mutual Economic Assistance (COMECON)”. These schools took place in Bulgaria and were chaired by Rotislaw Kaichev (Sofia) and Alexander Chernov (Moscow) and the working group supported always the participation of young researches of GDR. The general political situation has changed in February 1989 essentially initiated by Gorbatschow's politics of Perestroika. At the 23rd annual conference of VfK in Leipzig many speakers from western countries could be invited. From DGKK Klaus–Werner Benz (Freiburg), Elisabeth Bauser (Stuttgart), and Georg Müller (Erlangen) participated. Also from other Western European countries crystal growers came to Leipzig, as, for example, Raymond Kern (France), L. John Giling (The Netherlands), Roberto Fornari (Italy). Later in this year at the ICCG-9 in Sendai the “Crystal Growth Section of the Association of Crystallography – CGS/VfK” became a regular member of IOCG. This section was an integration of working groups “crystallization,” “industrial crystallization,” and “interfaces and thin layers.” The then president and secretary of the National Committee for Crystallography, Hermann Neels and Peter Rudolph, contributed very actively to the establishment of the section in the International Organization. Fast development of crystal growth in industry started during the fifties. The Philips Research Laboratory in Hamburg–Stellingen, founded 1957, was famous for ferri-magnetic materials with garnet structure and epitaxial layers for magnetic, magneto-optical, and detector applications. But also high melting oxides up to 1800 °C were grown from the melt by the Czochralski method (DGKK-Mitteilungsblatt Nr. 40, 1984). The crystal growth activities ended in 1990 when the research laboratory in Hamburg was closed. Another significant material group with crucial single crystal importance concerns the semiconductors. Directly after the Second World War the Siemens Cooperation started in Erlangen to develop semiconductor materials, like germanium, silicon, and compound semiconductors. The branch was headed by Eberhard Spenke and Walter Schottky. 1951 Heinrich Welker started his famous investigations of the III-V-semiconductors (for more details see the chapter of Jochen Friedrich and Georg Müller). In 1953 the research on high-purity silicon started in Burghausen followed by the semi-conductor production 1958. One year later the floating zone process was established. Then, in 1968 Wacker-Chemitronic GmbH was founded, which was renamed in 1994 into Wacker Siltronic GmbH. Now it is a stock company (Siltronic AG). The company was always engaged in the growth of electronic materials, namely silicon, InP, and GaAs. After the unification of Germany the growth of III-V compounds was moved to Freiberger Compound Material GmbH (FCM), whereas Siltronic GmbH was focusing on silicon. In addition to the traditional plant in Burghausen (Bavaria) Siltronic established a new branch for production of 12-inch (300 mm) silicon in Freiberg (2004). Today, both FCM and Siltronic are world-leading companies. Historically, at the beginning of sixties crystal growers were spread over many of the established societies acting there in sections and subgroups. Just to name some of them here: Deutsche Mineralogische Gesellschaft (DMG), Gesellschaft Deutscher Chemiker (GDCH), Deutsche Physikalische Gesellschaft (DPG), Bunsengesellschaft, Verein Deutscher Ingenieure (VDI). The crystal growers form a new section in one of the existing societies as, for example, DMG, DPG, GDCH, VDI. The crystal growers found a new and own society, for example, “Gesellschaft for Kristallzüchtung und Kristallisation” In spring 1969 a questionnaire was distributed among the people in this field. One third (of 150) voted for an own society. Most of the active crystal growers were in this group. The rest preferred a docking to one of the established societies. Founding an own group within the section “Kristallkunde” of DMG. Founding a free association of researchers Founding an own society with the option to be included in a German Society for Crystallography. A German Society for Crystallography did not exist during that time and the option was just for the case that such society would be founded. Several further discussions among the relevant persons led finally to the conclusion that the third option would be the best. On 9th July 1970 the meeting of the “Ausschuss Kristallisation” (committee crystallization) of the Verfahrenstechnischen Gesellschaft (VTG) within VDI took place in Bensheim-Auerbach, in which many crystal growers participated. That very evening a part of them met for the founding assembly of DGKK. In total of 13 members founded the Deutsche Gesellschaft für Kristallwachstum und Kristallzüchtung (German Association for Crystal Growth) as listed in Figure 2. The name of the association includes a peculiarity of the German language. There is the word Kristallwachstum for fundamental aspects of crystal growth and the one Kristallzüchtung for the growth of crystals. Siegfried Haussühl was elected as president and Rudolf Nitsche as his deputy. All former presidents and the present one are listed in Table 1. The Board of DGKK was firstly presented by photo in the second journal edition of the “Mitteilungsblatt” in 1983 (see Figure 3). The first general assembly took place in conjunction with the colloquium “Crystal Growth” of the German Research Foundation (DFG) in München on 15th October 1970. The membership had been increased to 73 personal members and three legal entities. Additional 13 persons joined DGKK during the colloquium. At this point it is worth mentioning that four years before the International Organization for Crystal Growth (IOCG) was founded by Michael Schieber. He noticed that such an International Organization would be much powerful with the support of national societies. Thus, in 1971 in total ten national societies became member of IOCG, besides those from France, Israel, Italy, Japan, The Netherlands, Spain, Switzerland, UK, USA also DGKK from Germany. Michael Schieber did not only found IOCG but also initiate the first International Conference on Crystal Growth (ICCG-1), which was held in June 1966 in Boston with a great success (625 participants). From that on ICCG was an important and prestigious event. In 1977 Kurt Recker proposed as the president of DGKK the German town Stuttgart for ICCG-7. The proposal was successful and 1983 Germany was the host for this international event. Another activity on national level was establishing an exhibition on crystal growth in the “Deutsches Museum” in München. Already in 1971 the board of DGKK fostered a small exhibition and the result was a showcase with single crystals, donated by members of DGKK. During reconstruction of the museum the objects were removed and suffered from water damage. The next attempt of DGKK was made in 1983. The museum planned to arrange an exhibition on mathematical instruments, computers, and micro-electronics. With the help on major donations from various companies and members of DGKK one room could be created with various objects from crystal growth. The new rooms were opened in May 1988. In the meantime, the museum has been rearranged again and the former exhibitions—also the one on crystal growth—were replaced by new ones based on modern concepts. Another direction of the DGKK activities is shown by the following: in the general assembly held 1986 in Erlangen Helmut Wenzl proposed to organize a bilateral Summer School with the colleagues in GDR. In particular, he made the suggestion to organize a school on “Epitaxy of Semiconductor Compounds” in Dresden in September 1987 (Minutes of the general assembly 1986). This would intensify the relations in a new way. He mentioned that BMFT (German Ministry for Research and Technology) would welcome this initiative. Rudolf Nitsche had already had some discussion with representatives in the GDR. Unfortunately, this idea was never realized. However, it shows the engagement for joint activities of east and west during that time. The first German Crystal Growth Conference after the fall of the wall took place in Frankfurt (Main) in March 1990. A large number of scientists from GDR attended this conference. Many also became a member of DGKK already in Frankfurt or shortly afterward. This was officially recognized during the general assembly during the next conference, 1991 in Gießen. During this time of dramatic changes Helmut Wenzl was the president of DGKK (1990–1993). His great personality enabled the successful integration of the crystal growers from the group “Kristallisation” of VfK. This was one reason that the working group, Kristallisation“ of VfK became obsolete. The other one was that the VfK founded together with the “Arbeitsgemeinschaft Kristallographie” (AGKr) the new society “Deutsche Gesellschaft für Kristallographie” (DGK) on 12th March 1991. From that time on we had DGK and DGKK presenting crystallography and crystal growth in Germany, respectively. Worth mentioning at this point is the journal “Mitteilungsblatt,” which has been published twice a year since 1983 (before it was a newsletter). During that time it had a section “Kristallzüchtung in Deutschland” (Crystal Growth in Germany). It was regarded as a good platform to present the locations of crystal growth in east and west. In parallel a number of new developments started in industry. The most important event after the German unification may be the foundation of Freiberger Electronic Werkstoffe GmbH, FEW in Freiberg out of the former “Spurenmetalle Freiberg”, SMF in 1990 and the transfer of the GaAs production (LEC) from Siltronic to FEW in 1991. Four years later the activities on III-V-compounds was transferred to the newly founded Freiberger Compound Materials GmbH (FCM) and FEW was integrated into Siltronic. Since that time a remarkable increase of quality in the growth of III-V-compounds was achieved by improvement of the Vertical Gradient Freeze method. In Idar–Oberstein, the research institute “Forschungsinstitut für mineralische und metallische Werkstoffe GmbH, FEE” was founded for the research and growth of single crystals based on Y-Al-Garnets (YAG) for laser or other (electro-)optical applications in 1990. Since 2018 it has been a part of the US-American company Electro-Optics Technology (EOT) (Mitteilungsblatt Nr. 68, 1998). For high-power electronic applications SiC has become a more and more important material. In Germany it is the SiCrystal GmbH in Nürnberg, which grows the SiC crystals up to 150 mm from the vapor phase. It was founded 1996 from outsourcing the SiC growth from the University of Erlangen. Huge but short activities happened in photovoltaics, mainly the growth of silicon, RWE Schott Solar GmbH, Deutsche Solar GmbH, or Solar World GmbH as well as of CuIn2S4 by Würth Solar GmbH & Co. KG, Schwäbisch Hall until the crash of photovoltaic business around 2010 finished most of the companies in Germany. Another branch of crystal growth was filled by Schott Lithotec AG (starting 1998 as a subsidiary of Schott Glas in Mainz, now in Jena): huge CaF2 crystals up to 100 kg within 8 weeks for stepper lenses and other optical devices were grown. Since 1976 IR technology is hosted in Heilbronn, initially by AEG-Telefunken, later by the outsourced company AIM Infrared Module GmbH (1996). For this kind of modules, crystals and epitaxial layers of II-V–compounds, such as (Cd,Zn)Te and (Hg,Cd)Te are produced. Last but not least large high-quality Ge crystals are manufactured at Photonic Sense GmbH in Eisenach. An important date for crystal growth research in Germany was 1st January 1992 when the Institute for Crystal Growth (IKZ) was founded in Berlin Adlershof, based on the former GDR institutes “Technikum für Kristallzüchtung” of the former, Zentrums für wissenschaftlichen Gerätebau (ZWG)” of the Akademie der Wissenschaften” together with the groups for crystal growth of II-VI-compounds of the “Zentralinstituts der Elektronenphysik (ZIE)” and the groups for oxide crystals of the “Zentralinstituts für Optik und Spektroskopie (ZOS).” Winfried Schröder became the director of the institute and in 1994 the first DGKK president from the east part of Germany. As a member of the Leibniz Society the institute included the term “Leibniz” 2008 into the name and is “Leibniz-Institut für Kristallzüchtung” today. It is one of the leading institutes for crystal growth in Europe and worldwide. Despite the fact that research in crystal growth is reduced at many academic places there is still a reasonable number of students and young researchers in the field of crystal growth. In order to be better presented they organized themselves as ”young DGKK” (jDGKK) in 2012. They organize every year a symposium a day before the annual conference of DGKK and 2019 the 1st joint meeting together with the “young crystallographers” (jDGK), was organized in Köln. The Annual Conference on crystal growth is as old as the association itself. The first conference was organized at the University of Bonn in 1971. Since that time the conference on crystal growth has been held every year—sometimes in conjunction with the European or International conference. The list of all conferences is shown in Table 2. Often the conference was organized with other societies in Germany as Arbeitsgemeinschaft für Kristallographie (AGKr), later the Deutsche Gesellschaft für Kristallographie (DGK), Deutsche Physikalische Gesellschaft (DPG) or in the neighboring countries like Assoziazione Italiano di Crescita dei Cristalli (AICC), British Association for Crystal Growth (BACG), The Czecheslowak Association for Crystal Growth (CSACG), Group Français de Croissance Cristalline (GFCC), Kontaktgroep Kristalgroei Nederland (KKN), Polish Society for Crystal Growth (PSCG), and Section Crystal Growth of Swiss Society for Crystallography (SKW). Already the founders of DGKK were aware of the importance of an annual conference for exchanging results and ideas. They put the task of ensuring the organization of the conference every year as an obligatory task for the council into the by-law. Such a conference was also an excellent opportunity to meet with colleagues from the neighboring countries and many joint conferences were organized during the years. GaAs and other III-V compounds CdTe (II-VI compounds) Oxides Epitaxy of semiconductors Support of young researchers They should be seen as a seed for establish working groups when successful. In November 1986 a symposium on epitaxy was held in Stuttgart at Standard Elektrik Lorenz AG (SEL) organized by Peter Speier with in total 30 participants. Twice, in March 1987 and October 1987 symposia on III-V compounds took place at Siemens AG in Erlangen. For these two events with about 60 participants Georg Müller was responsible. Thus, two working groups were established, which have been acting very successful until today. Epitaxy of semiconductors was later restricted to epitaxy of III-V compounds but nevertheless the meetings are the largest among all working groups (about 100 participants). The working group on GaAs and other III-V compounds were dominated in the nineties by the development of industrial processes for GaAs and also InP single crystals. Characterization and their methods played a significant role for understanding the defects, which was a prerequisite for improving the crystal quality. In the years 2000 SiC, GaN, and also AlN emerged to become important materials for power and opto-electronics and were included. At the end of the 2000s there was this hype in the PV market and many growers moved to multi-crystalline or mono silicon for PV applications. Therefore, the topics were extended by this subject. The first meeting on II-VI compounds took place in 1986 in Würzburg with 25 participants followed by another one in March 1988 at University Karlsruhe. At that time German Müller–Vogt was responsible for this working group. It appeared that thin layers of II-VI compounds became more and more important and not many researchers in Germany worked on bulk crystal growth. There were a lot of activities also by other communities, for example, a priority programme was established by the German Science Foundation, a European Workshop on II-VI semiconductors was organized regularly. Therefore, extra activities by DGKK were not necessary. On the contrary, the topic of oxide crystals, especially for lasers and non-linear optics, is today as important as it was at the end of the eighties. The first symposium was organized 1987 at the University Osnabrück. Three years later the working group “oxides” was founded at the general assembly in Frankfurt/Main 1990. Major players were Wolfgang Tolksdorf from Philips in Hamburg, Hans-Josef Paus in Stuttgart (who got part of the growth equipment from Philips in 1990) and Lothar Ackermann from FEE Idar–Oberstein. Already colleagues from the former GDR joined the group mainly from the former “Zentralinsitut für Optik und Spektroskopie” (ZOS) and Carl Zeiss (Jena). The first meeting was organized by Hans-Josef Paus at the Institute of Physics at the University Stuttgart. The portfolio of materials for laser and non-linear optics was very broad. Such kind of materials have been also investigated in France and consequently Lothar Ackermann proposed to invite also colleagues from France. Since that time the workshop is organized alternating in Germany and France. A more fundamental subject is growth kinetics. It has been noticed that there were many activities in the Netherlands in this field but it was not clear, which work was done in Germany. The researchers in this field were spread over different places and disciplines, and only a few were member of DGKK at that time. Therefore, a workshop on this topic was organized in 2000 by Peter Rudolph. It appeared that indeed there was a lot of interesting research in this field going in Germany. From dendritic growth to step bunching in epitaxy, from real-time observations of eutectic solidification to multi-scale simulations of epitaxial growth, there was broad spectrum of contributions by experts from an interdisciplinary environment. On the contrary, there are also topics closely related to industrial crystal growth. Therefore, in 2013 a new working group was founded by Albrecht Seidl (Industrial Crystal Growth). The idea was to address more general topics relevant to industrial processes of crystal growth rather than to deal with particular growth processes or brand new results. The first edition was on high-temperature materials for crystal growth. Another focused on the important subject how to measure during the industrial growth process and how to control. The success of these workshops showed that there are still many companies in Germany, which are active in this field. With increasing computer power during the nineties numerical calculations of the growth process became feasible and thus an emerging topic of research and development. Consequently, a new working group was created by Albrecht Seidl in 2000: “Applied Numerical Simulation.” It is worth mentioning that the initiative came from researchers in industry. It was of great interest for the companies active in crystal growth to learn what could be computed and how could this improve the process development. The workshops were attended by engineers and crystal growers from industry, experimental researchers, researchers doing simulation, and mathematicians. It was the time of developing codes with sufficient stability and flexibility but also with an easy-to-use interface. After twelve years the main development was completed and using numerical calculations for process development has become a standard. There are still challenges, especially with emerging topics like artificial intelligence but this requires a different character of the workshop. Today, in the thirtieth year after the “Wall was broken,” the DGKK is a beautiful, unified, very active, and internationally highly respected association joining about 400 members from whole Germany and even abroad working in the fields of crystal growth, preparation, epitaxy, and analysis. Figure 4 shows a large DGKK delegation at the ICCGE-16 in Beijing 2010.

Basal plane dislocations (BPDs) in 4H silicon carbide (SiC) crystals grown using the physical vapor transport (PVT) method are diminishing the performance of SiC-based power electronic devices such as pn-junction diodes or MOSFETs. Therefore, understanding the generation and movement of BPDs is crucial to grow SiC suitable for device manufacturing. In this paper, the impact of the cooldown step in PVT-growth on the defect distribution is investigated utilizing two similar SiC seeds and identical growth parameters except for a cooldown duration of 40 h and 70 h, respectively. The two resulting crystals were cut into wafers, which were characterized by birefringence imaging and KOH etching. The initial defect distribution of the seed wafer was characterized by synchrotron white beam X-ray topography (SWXRT) mapping. It was found that the BPD density increases with a prolonged cooldown time. Furthermore, small angle grain boundaries based on threading edge dislocation (TED) arrays, which are normally only inherited by the seed, were also generated in the case of the crystal cooled down in 70 h. The role of temperature gradients inside the crystal during growth and post-growth concerning the generation of shear stress is discussed and supported by numerical calculations.

This article describes complete characterization of the polygonal dislocation half-loops (PDHLs) introduced by scratching and subsequent bending of an Si(111) crystal. The study is based on the X-ray topo-tomography technique using both a conventional laboratory setup and the high-resolution X-ray image-detecting systems at the synchrotron facilities at KIT (Germany) and ESRF (France). Numerical analysis of PDHL images is performed using the Takagi–Taupin equations and the simultaneous algebraic reconstruction technique (SART) tomographic algorithm.

We present in-situ observations of the dynamical operation of multiple double-ended Frank-Read dislocation sources in a PVT-grown 4H-SiC wafer under thermal gradient stresses. The nucleation of these sources is facilitated by a specific configuration consisting of one basal plane dislocation (BPD) segment pinned by two threading edge dislocations (TEDs). This configuration is formed during PVT crystal growth by deflection of TEDs on to the basal planes by macrosteps and re-deflection of resulting BPDs back into TEDs. Under the influence of thermal gradient stresses induced by heating inside a double ellipsoidal mirror furnace, the pinned BPD segment glides and activates dislocation multiplication by the double Frank-Read source mechanism. A more intricate mechanism of swapping of TED pinning points between Frank-Read sources lying on same basal plane is identified, enabling one dislocation loop to effectively “pass through” the other dislocations on same basal plane.

Coesite and stishovite are high‐pressure silica polymorphs known to have been formed at several terrestrial impact structures. They have been used to assess pressure and temperature conditions that deviate from equilibrium formation conditions. Here we investigate the effects of nonhydrostatic, dynamic stresses on the formation of high‐pressure polymorphs and the amorphization of α‐quartz at elevated temperatures. The obtained disequilibrium states are compared with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We analyzed phase transformations starting with α‐quartz in situ under dynamic loading utilizing a membrane‐driven diamond anvil cell. Using synchrotron powder X‐ray diffraction, the phase transitions of SiO 2 are identified up to 77.2 GPa and temperatures of 1160 K at compression rates ranging between 0.10 and 0.37 GPa s −1 . Coesite starts forming above 760 K in the pressure range between 2 and 11 GPa. At 1000 K, coesite starts to transform to stishovite. This phase transition is not completed at 1160 K in the same pressure range. Therefore, the temperature initiates the phase transition from α‐quartz to coesite, and the transition from coesite to stishovite. Below 1000 K and during compression, α‐quartz becomes amorphous and partially converts to stishovite. This phase transition occurs between 25 and 35 GPa. Above 1000 K, no amorphization of α‐quartz is observed. High temperature experiments reveal the strong thermal dependence of the formation of coesite and stishovite under nonhydrostatic and disequilibrium conditions.