An overview of selected contributions to the development of crystal growth technology of the Laudise Prize awardee 2023 is presented. First some results on shaped crystal growth are given, such as layers with eutectic periodic structures, casting of high-resistivity CdTe sheets, growth of in situ core doped laser rods by double die EFG, and Czochralski growth of Si crystals with rectangular cross section. Then the correlation between melt structure and quality of II-VI crystals showing high bond ionicity is discussed. The importance of marked melt overheating for growth of high-quality CdTe and (Cd,Zn)Te crystals is derived. Also the in situ stoichiometry control for reducing intrinsic point defects, precipitates and inclusions is demonstrated by the examples of Bridgman and VGF CdTe growth with Cd extra source and vapor pressure controlled Czochralski method of 6 inch GaAs crystals. Next, the reason and general appearance of dislocation cell patterns in all growing thermomechanical stressed crystals and their possible prevention are explained. The contribution of point defect diffusion for dislocation climb at high temperatures to form globular cells is underlined. Finally, melt growth experiments under travelling magnetic field (TMF) generated in coil-shaped heater-magnet modules around the crucibles are discussed. The importance of global numeric modeling for optimization the TMF convection mode in the melt is accentuated. It is shown that the growing interface can be levelled, the solution flux at vertical liquid phase epitaxy can be homogenized, and the IR transmission and minority carrier live time in 640 kg mc-Si ingots for photovoltaics can be markedly enhanced and homogenize by such external field application. The close cooperation between academics, engineers and industry is particularly emphasized.

The difference in the crystallization kinetics during growth from the melt between II–VIs (CdTe, Cd1−xZnxTe, ZnSe, and ZnTe) and III–Vs (GaAs and InP) is discussed. At the melt growth of II–VI crystals, the most important difference is the lack of controllability of seeding and achievement of a desired growth orientation. A pronounced tendency of self-orientation toward <111>, <110>, and sometimes <112> and <122>, but almost never toward <100> direction, has been observed regardless of whether a seed has been used or not. The main reason proves to be the tetrahedral coordination due to the high binding ratio of ionicity remaining in the II–VI melts but not occurring in III–Vs. As a result, the general effect of pre-ordering into density layers, forced by the solid surface, is in the II–VI liquids superimposed by a {111} self-orientation via tetrahedral in-plane alignment. Fitting growth kinetics seem to only be possible when this melt configuration conforms to the crystal structure, like the {111} but hardly the {100}. Otherwise, the liquid self-orientation determines the continuing crystal orientation. Additionally, an <100>-oriented seed abruptly changed into an <122> direction via a congruent twin plane. Although such considerations still need verifying atomistic simulations, they are helpful to optimize the growth methodology even for larger crystal diameters.

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.

The recent development of semiconductor crystal growth focusses on increase of process efficiency and simultaneous improvement of crystal quality. For improved crystal quality, an exact and permanent control of the melt flow is a crucial parameter. To achieve larger crystals, the melt volume must be increased markedly resulting in disadvantageously changed melt convection. In the case of Czochralski growth, the flow can even become turbulent. This changed flow can disturb the single crystal growth and may give rise to dopant inhomogeneities within the crystal. To effectively influence melt flow and hence to improve growth conditions, magnetic fields can be applied. Mostly, steady magnetic fields (SMF) are applied in industrial scale to damp melt flow oscillations. However, compared to SMF the application of non‐SMF proves to be also very promising since significantly lower induction causes similar effects in the melt. An overview on magnetic field features with the focus on achievable results under the influence of traveling magnetic fields is given.

An overview of the important defect types, their origins and interactions during the bulk crystal growth from the melt and selected epitaxial processes is given. The equilibrium and nonequilibrium thermodynamics, kinetics and interaction principles are considered as driving forces of defect generation, incorporation and assembling. Results of modeling and practical in situ control are presented. Strong emphasis is given to semiconductor crystal growth since it is from this class of materials that most has been first learned, the resulting knowledge then having been applied to other classes of material. The treatment starts with melt-structure considerations and zero-dimensional defect types, i.e. native and extrinsic point defects. Their generation and incorporation mechanisms are discussed. Micro- and macro-segregation phenomena – striations and the effect of constitutional supercooling – are added. Dislocations and their patterning are discussed next. The role of high-temperature dislocation dynamics for collective interactions, like cell structuring and bunching, is specified. Additionally, some features of epitaxial dislocation kinetics and engineering are illustrated. Next the grain boundary formation mechanisms, such as dynamic polygonization and interface instabilities, are discussed. The interplay between facets, inhomogeneous dopant incorporations and twinning is shown. Finally, second phase precipitation and inclusion trapping are discussed. The importance of in situ stoichiometry control is underlined. Generally, selected measures of defect engineering are given at the end of each sub-chapter.

We performed 3D numerical and experimental studies to assess the potential of peripheral low frequency mechanical vibrations for improving the homogeneity of Sb-doped 4″ Ge crystals grown by vertical gradient freeze (VGF). For this study, a novel bell-shaped graphite vibrator was developed for the generation of the axial vibrations in the direction of three-phase junction. Melt stirring by downward traveling magnetic field (TMF) was used as a benchmark.The results showed superiority of peripheral vibrations to TMF stirring concerning radial and longitudinal doping distribution and initial stirring rate. Experimentally observed standing free surface waves in Ge were caused by shielding effect of the vibrator on TMF.

The quality of single crystals, epitaxial layers and devices made there from are very sensitively influenced by structural and atomistic deficiencies generated during the crystal growth. Crystalline imperfections comprise point defects, dislocations, grain boundaries, second-phase particles. Over more than a half-century of the development of crystal growth, most of the important defect-forming mechanisms have become well understood [1-2]. As a result, the present state of technology makes it possible to produce crystals of remarkably high quality. However, that is not to say that all problems are already solved. For instance, in comparison with silicon the point defect dynamics in semiconductor and oxide compounds is not nearly as well understood. The density of equivalent defect types and antisites in each sub-lattice is determined by deviation from stoichiometry. Their charge state depends on the Fermi level position leading via interaction with dopants to certain compensation level and complex formation. One measure proves to be the in situ control of stoichiometry. Due to high-temperature dislocation dynamics heterogeneous dislocation substructures are formed. Both, acting thermo-mechanical stress and given point defect situation force the dislocation to glide and climb. In the course of enthalpy minimization the long-range character of dislocation interaction produces agglomerates and patterns with polygonized cell walls, i.e. small angle grain boundaries [3]. Thanks to the rules of correspondence of Taylor and Kuhlmann-Wilsdorf one is able to estimate the interaction between shear stress, dislocation density and cell diameter (Fig.). In epitaxy the Nye tensor, describing dislocation distribution inhomogeneity, affects the layer stress considerably. The growth under minimum stress, solution hardening and in situ stoichiometry control are effective counteracting methods. One of the most serious consequences during cooling down of as-grown crystals is the point defect condensation in precipitates and micro-voids decorating dislocation patterns or inducing high mechanical misfit stress that generates dislocation loops. It proves to be favourable to anneal the crystal a few degrees below the melting point in order to dissolve the particles and re-diffuse their into the crystal matrix.

A numerical comparison of various techniques of non-steady magnetic stirring, such as travelling (TMF), rotating (RMF), alternating (AMF) and carousel magnetic fields (CMF), during unidirectional solidification of large rectangular silicon melts of 700 kg was performed. The comparison was focused on the time required to homogenize the distribution of a point wise released tracer in the melt. All studied magnetic fields showed identical magnetic screen and interaction parameter R-omega=80.3 and N-mag =7.9 x 10(-6), respectively. The Lorentz forces were generated in KRISTMAG (R) heater magnet modules (HMM) positioned at the side or bottom of the silicon melt container. Stirring progress was studied by tracking the formation of the concentration field of the passive tracer in already fully developed melt flow. Results revealed the superiority of the CMF concept independent of the point of injection. (C) 2012 Elsevier B.V. All rights reserved.

Traveling magnetic fields (TMFs) can be used to control the shape of the crystal–melt interfaces at crystal growth from melt. Here, we present the numerical results of a systematic study on the influence of a TMF generated by a KRISTMAG˜® heater-magnet module on the interface curvature of different materials varying in their electrical conductivity in a wide range (5×101 to 1.7×107S/m) such as Ge, Si, CdTe, BaF2 and YAG. Materials were compared in the same design of environment by using results obtained for Ge as a reference. For the rescaling of the growth equipment, non-dimensional criteria were applied. Positive slightly convex crystal–melt interface can be obtained for all materials studied using moderate electrical currents.

A novel electro-magnetic stirring approach using Carousel magnetic fields (CMF) generated by bottom multifunctional KRISTMAG® heater magnets is proposed for directional solidification of large silicon ingots for photovoltaics (PV) with mass of 700kg. 3D numerical simulations were performed for Reynolds, Rayleigh and magnetic Taylor numbers in the range from Re=7.044×103–2.123×104, Ra=2.0083×109–2.0096×109 and Tamag=5.26×109–3.79×1010, respectively. Stirring progress was studied by tracking the volume average velocity, vorticity and temperature in the melt using buoyancy driven flow as a benchmark.The numerical results show advantageous enhanced mixing by CMF even along the melt cross section parallel to the solidification front and axial flow intensification parallel to the growth direction, particularly in the bottom melt region without dangerous acceleration of the flow in the vicinity of the crucible side walls.

We have performed 3D calculations of the melt flow during Czochralski growth of nearly square-shaped silicon crystals by means of Ansys-cfx. Beforehand, the temperature field in the furnace has been computed by axisymmetric computations using CrysMAS for providing thermal boundary conditions for the local simulation of the melt flow. CrysMAS has been also used for the computations of Lorentz force densities, produced by a travelling magnetic field using the KRISTMAG˜® approach.

Conventionally grown Czochralski (Cz) silicon crystals for photovoltaic (PV) application have an unfavourable cylindrical shape leading to essential material loss during the wafer cutting process. Additionally, the typical high oxygen concentration promotes solar cell degradation. In this paper a new pulling technology for growth of silicon crystals with both quadratic cross section and relatively low as-grown oxygen content is presented. A dynamic-magnetic-field-assisted Cz growth of facetted crystals is reported. At [0 0 1]-oriented growth in very low radial temperature gradient holding steady by a special traveling magnetic field (TMF) the growing crystal body becomes self-profiling by four {1 1 0} facets parallel to the pulling direction. To keep down costs the KRISTMAG˜® principle was used whereupon the Lorentz field and heat are simultaneously generated within a graphite heater design supplied by alternating (AC) multiphase current of various frequencies and phase shifts. The first experimental results show single crystalline Si crystals with reproducible square cross sections up to 91×91 mm2 including rounded corners. Until now TMF frequencies of f=180 and 300 Hz and a phase shift of φ=90° were applied. For high-purified material an average facet undercooling of ΔT≈2 K has been deduced from the observed rectangular side plane widths. According to high-resolution transmission electron microscopy (HRTEM) the four macroscopically flat faces are microscopically composed of {1 1 0} sub-facets and {1 1 1} macrosteps. Etch pit densities (EPD) between 0 and 104 cm−2 were ascertained. Due to the magnetically induced high-speed melt flow toroid around the growing crystal a relatively low and homogeneously distributed oxygen concentration can be achieved. A minimum value of 7.5×1017 cm−3 was measured in high-purity as-grown crystals at a TMF frequency of f=300 Hz.

Selected fundamentals of transport processes and their importance for crystal growth are given. First, principal parameters and equations of heat and mass transfer, like thermal flux, radiation and diffusion are introduced. The heat-and mass-balanced melt-solid and solution-solid interface velocities are derived, respectively. The today's significance of global numeric simulation for analysis of thermo-mechanical stress and related dislocation dynamics within the growing crystal is shown. The relation between diffusion and kinetic regime is discussed. Then, thermal and solutal buoyancy-driven and Marangoni convections are introduced. Their important interplay with the diffusion boundary layer, component and particle incorporation as well as morphological interface stability is demonstrated. Non-steady crystallization phenomena (striations) caused by convective fluctuations are considered. Selected results of global 3D numeric modeling are shown. Finally, advanced methods to control heat and mass transfer by external forces, such as accelerated container rotation, ultrasonic vibration and magnetic fields are discussed.

This chapter gives an overview of the important defect types and their origins during bulk crystal growth from the melt. The main thermodynamic and kinetic principles are considered as driving forces of defect generation and incorporation, respectively. Results of modeling and practical in situ control are presented. Strong emphasis is given to semiconductor crystal growth since it is from this class of materials that most has been first learned, the resulting knowledge then having been applied to other classes of material. The treatment starts with zero-dimensional defect types, i.e., native and extrinsic point defects. Their generation and incorporation mechanisms are discussed. Micro- and macrosegregation phenomena – striations and the effect of constitutional supercooling – are added. The control of dopants by using the nonconservative growth principle is considered. One-dimensional structural disturbances – dislocations and their patterning – are discussed next. The role of high-temperature dislocation dynamics for collective interactions, such as cell structuring and bunching, is shown. In a further section second-phase precipitation and inclusion trapping are discussed. The importance of in situ stoichiometry control is underlined. Finally two special defect types are treated – faceting and twinning. First the interplay between facets and inhomogeneous dopant incorporation, then main factors of twinning including melt structure are outlined.

Many concepts of external magnetic field applications in crystal growth processes have been developed to control melt convection, impurity content and growing interface shape. Especially, travelling magnetic fields (TMF) are of certain advantages. However, strong shielding effects appear when the TMF coils are placed outside the growth vessel. To achieve a solution of industrial relevance within the framework of the project inner heater-magnet modules(HMM) for simultaneous generation of temperature and magnetic field have been developed. At the same time, as the temperature is controlled as usual, e.g. by DC, the characteristics of the magnetic field can be adjusted via frequency, phase shift of the alternating current (AC) and by changing the amplitude via the AC/DC ratio. Global modelling and dummy measurements were used to optimize and validate the HMM configuration and process parameters. GaAs and Ge single crystals with improved parameters were grown in HMM-equipped industrial liquid encapsulated Czochralski (LEC) puller and commercial vertical gradient freeze (VGF) furnace, respectively. The vapour pressure controlled Czochralski (VCz) variant without boric oxide encapsulation was used to study the movement of floating particles by the TMF-driven vortices.

For the first time semi-insulating (SI) GaAs single crystals were grown by the liquid encapsulated Czochralski (LEC) method using a traveling magnetic field (TMF) system generated in a heater–magnet module (HMM). The system was developed within the framework of the KRISTMAG˜® project. The HMM, that generates heat and TMF simultaneously, was placed closely around the crucible inside the chamber of the industrial CI 358 puller. Before the growth experiments the induced vertical Lorentz force density FLz was evaluated by the weight force response of a dummy. First growth experiments at various f/ϕ ratios (f—frequency and ϕ—phase shift) were carried out. Interface morphology and temperature fluctuation strengths were analyzed by a striation technique. Etch pit density, carbon, residual impurity and EL2° contents as well as electrical properties of the as-grown TMF–LEC GaAs crystals were measured. A preliminary correlation between crystal qualities and field frequency has been noticed.

We present numerical simulations of liquid encapsulated Czochralski crystal growth of GaAs under the influence of a travelling magnetic field. As described in Rudolph 2008 (Proceedings for ICCG-15), the magnetic field is generated by an internal heater-magnet module, replacing the usual heater units inside the pressure chamber in the growth arrangement. We consider two possible realizations of the heater-magnet and numerically investigate the influence of the Lorentz force on the melt, e.g., the damping of the temperature oscillations in the Taylor cell below the crystal. This work has been conducted in the project KRIST (MAG) over tilde (R) framework, see http://www.kristmag.com/, which has been awarded with the Innovationspreis (innovation prize) Berlin-Brandenburg 2008.