Workshop on crystal growth technology

Beatenberg, Switzerland, September 2005

The Third Int’l Workshop on Crystal Growth Technology (IWCGT-3) was held in Beatenberg, Switzerland, September 10-18, 2005. 38 speakers lectured on research and numerical simulation of crystal growth processes, crystal growth industry, crystal machining and crystal characterization. Approximately 90 crystal growers and technologists from 12 different nations, some of them with their families, attended the workshop.

The opening lecture on the growth of large halide scintillation crystals up to 450 kg weight was by A. Gektin (Inst. of Single Crystals, Kharkov, Ukraine). J. Telfer (Hilger Crystals Ltd, UK) gave an overview on crystal growth in the UK, focusing also on scintillation crystals. K. Jacobs (Inst. for Crystal Growth IKZ, Berlin, Germany) introduced the thermodynamics of crystal production processes from melt, solution and vapor. M. Mühlberg (U. of Cologne) followed up with phase diagrams as useful tools for crystal growth. The growth techniques of large (6 inch diameter) Nd-doped GGG-crystals (Gd-Ga-Garnet, Gd₃Ga₅O₁₂) as well as of the classical garnets for high power lasers were presented by M. Randles (Northrop Grumman Synoptics, Charlotte, NC, USA). The series of talks on semiconductors was started by F. Börner (Freiberger Compound Materials FCM), who gave an overview on GaAs, focusing on its markets now and then, the production and future of wafers, and the economy of GaAs industry. Y. Makarov (Semiconductor Technology Research Inc. Richmond, VA, USA), presented a model for the Czochralski growth of large Si crystals in industrial systems, applying or not magnetic fields. F. J. Bruni (Santa Rosa, CA, USA) also talked on the Czochralski method, presenting ways to control the diameter and the interface shape stability of large industrial Si crystals, as well as lithium niobate and tantalate, GGG. The first day was closed with a panel discussion on world-wide crystal production.
P. Capper (Selex Sensors and Airborne Systems Infrared Ltd, Milbrook, UK) spoke on the use of forced mixing by acceleration of crucible rotation (ACRT H.J. Scheel 1971) in the Bridgman technique for CMT (Cd-Hg-Telluride, CdxHg1-xTe) used in infrared detectors. J.J. Derby (U. of Minnesota) introduced the possibilities of simulating flow effects during crystal growth as compared with the state of the art in modeling melt and solution crystal growth processes. K. Kakimoto (Kyushu U., Japan) analyzed the effects of magnetic field configuration on the melt-crystal interface shape and melt flow during the growth of a Si-crystal obtained via the Czochralski method, whereas T. Hibiya (Tokyo Metropolitan U.) gave an overview of the thermophysical properties of crystal growth melts. K. Schaffers (Lawrence National Lab., Livermore, CA, USA) talked on the growth or large laser crystals for fusion energy, highlighting the current problems of crystalline materials, and the largest YCOB-crystals (= YCa₄O{BO}₃) that could be produced so far. She was awarded best speaker of the conference for her talk. S. Uda (Tohoku U., Japan) presented the crystal growth of langasite-type crystals and their device properties. V.A. Klipov (Sawyer Technical Materials, Eastlake, OH, USA) dealt with the hydrothermal production of quartz crystals. A second talk by Y. Makarov on the modeling analysis of vapor pressure-controlled Czochralski Growth of GaAs bulk crystals and other low-gradient crystal pulling concluded the series of presentations of the second day.
After a full-day excursion onto the Faulhorn, P. Rudolph (IKZ Berlin, Germany) started the day with a review on defects, their thermodynamics, origin and characterization. J. Friedrich (Fraunhofer Inst. Erlangen, Germany) combined thermal modeling with experimental studies of the vertical gradient freeze technique for the synthesis of large industrial semiconductor crystals, focusing on the example of InP. His talk was followed by a contribution by S. Eichler (FCM, Germany), who explained first the different crystal growth techniques of GaAs, followed by methods of doping for micro-electronics and opto-electronics. Then, A. Mühe (Crystal Growing Systems GmbH, Asslar, Germany), gave insights into the design of crystal growing systems, focusing on the interplay of material sciences and economy. Industrial crystal growth technologies of III-V compound semiconductors including GaN were presented by M. Tatsumi (Sumimoto Electric Industries, Japan). In-doped GaSb solid solution crystal growth using the vertical Bridgman technique with ACRT was discussed by P. S. Dutta (Rensselaer Polytechnic Inst., NY, USA). He was followed by G. Siefer (The Fraunhofer Inst. for Solar Energy Systems, Freiburg, Germany), who presented a new type of solar cell, Flatcon, based on III-V tandem cells and using a concentrator system, he explained its performance as compared with traditional solar cells. H. Scheel (Beatenberg, Switzerland) concluded the talks with a discussion on saving energy and renewable energy in which crystal growth technology can play a crucial role. The day ended with a panel discussion on that very subject.
The next day, dedicated to crystal machining, started with an animated presentation by H.J. Moeller on the physics of crystal sawing technology focusing on processes happening at the crystal surface upon different modes of multi-wire sawing and properties of the final products. P. Nasch (HCT Shaping Systems, Switzerland) gave a historical overview of multi-wire slurry slicing techniques for silicon crystals, and described the recent technology with examples and analysis. Y. Sano (Osaka U., Japan) introduced the technique of plasma chemical vaporization machining (PCVM) applied to SiC and Si crystals, and it was shown that this method allows slicing with a precision down to 7 nm. His colleague, K. Yamauchi, presented the revolutionary elastic emission machining (EEM) that is used for the generation of ultra-flat and crystallographically well-ordered surfaces of functional materials, such as total reflection X-ray mirrors. Over lunch time, a general assembly of the board of the Section of Crystal Growth and Technology of the Swiss Society of Crystallography was held in the presence of interested persons from the Swiss crystal industry in order to discuss the future of industrial crystal growth in Switzerland. In the afternoon, two lectures were given. The first one by F. Schmid (Crystal Systems Inc., Salem, MS, USA) dealt with the new technique of improved multi-wire slicing with fixed abrasive slicing technology (FAST) for cutting sapphire and SiC used in LED applications. J. Neugebauer (Max Planck Inst. Düsseldorf, Germany) uses DFT methods with concepts of thermodynamics, continuum theory and/or statistical mechanics. He presented applications to microscopic growth mechanisms, as well as limits of the method. The crystal growth prize, as well as the crystal technology prize of the Section of Crystal Growth and Technology of the Swiss Society of Crystallography were awarded by H. Scheel to Shintaro Miyazawa (Waseda U., Japan) for his contributions to crystal growth and epitaxy technologies and for establishing the role of dislocations for GaAs micro- and optoelectronics, and to Yuzo Mori (Osaka U., Japan) for his development of PCVM and EEM, respectively. This ceremony took place during the banquet at the Hotel Jungfrau-Victoria in Interlaken. Another full-day excursion onto a glacier, together with a glaciologist from ETH Zurich, was organized on Friday. The scientific program continued on Saturday with D.K. Bowen (Bede Scientific Inc., Englewood, UK), who presented on high precision digital X-ray diffraction imaging for quality analysis of industrial crystals before further processing, which is an important market due to the very high price of large crystals. D. Bliss (US Air Force Research Lab. and President of the American Crystal Growth Assn) highlighted recent advances in InP bulk crystal growth, focusing on the special care to be taken in order to avoid formation of white phosphorous during crystallization conditions, and the influence of dopants upon twinning. His talk was followed by G. Wehrhan (Schott Lithotec AG, Germany), who presented the recent development in CaF₂-production used in optical lenses for UV lithography. Also dealing with CaF₂, Y. Oyama (Canon Research Center, Japan) discussed the Bridgman technique and other production methods of large crystals, presenting various results of physical parameters of CaF₂ and its melt. H. Scheel and L. Lytvynov shared a talk on the flame-fusion (Verneuil) growth of oxides before W. Assmus (U. of Frankfurt am Main, Germany) gave an overview on the skull melting of zirconia, ZrO₂, which is widely used as an imitation gem stone for diamond, highlighting the special conditions under which this material of 2700º C melting point can be obtained. Liquid phase epitaxy, LPE, is used for large rare-earth iron garnet layers, as presented by T. Iino (Sumitomo Metal Mining, Japan). The final talk was given by F. Dupret (U. Catholique de Louvain, Belgium) on numerical modeling of different aspects of industrial crystal production, using the software FEMAG. Finally, the conference ended in the evening with a panel discussion on the future of crystal growth and the awarding of the three best lecturers of the conference.

Overall, H. Scheel and his wife R. Hauser-Scheel have put together an appealing and successful conference with an intensive, high-level, and interdisciplinary scientific program, and a perfectly well organized social and ladies program. Many participants expressed their hopes for a future workshop to be held in this region, so we all look forward to IWCGT-4 to be held in 2008.

The Book of Lecture Notes of this workshop can be ordered at a cost of $50 from Hans Scheel, hans.scheel@bluewin.ch, and the full papers of most lecturers will be published in the planned book Crystal Growth Technology II (editors P. Capper and H.J. Scheel, Wiley and Sons 2006).

Katharina M. Fromm