Preface - Vapour growth of bulk crystals and expitaxy - Part I

Crystal growth from the vapour is of paramount importance in modern materials science. This is especially true in the technology of electronic, optical and electrooptical devices that rely for their performance on single crystal structures. Vapour growth processes play a crucial role in epitaxial-layer deposition techniques such as PVD, CVD, MOCVD, MBE, and are further being emphasized by the discovery of nano-structure associated quantum effects, whose exploitation has resulted in the creation of almost unique devices. Also, vapour growth, in the case of bulk (volume) crystals, continues to attract increasing interest and must not be overlooked, even if most industrial production still relies on melt growth and is very likely to remain so in the near future. The lack of high-quality substrates is still a severe limitation in the development of many advanced electronic devices and alternative methods to melt growth are being successfully investigated. The numerous vapour growth experiments in microgravity, as promoted by the various space agencies in many countries, are here relevant. Interest in vapour growth has, however, a more general explanation. As is well known, the usefulness of single crystals, when compared with polycrystalline and amorphous materials, stems from the ability to provide media in which the mobility of electric charge carriers and the general optical quality are so much the more enhanced, the more perfect is the crystal. Now, as this enhancement in real crystals increases with the decrease of structural defects and compositional inhomogeneities in the lattice, the importance of vapour-grown crystals becomes evident when considering that their crystallization temperatures are significantly lower than their melting points and, consequently, the thermally activated processes that negatively affect the final crystal quality are as a rule slowed down and partially hindered. Therefore, under optimized growth conditions and in a comparison with the same crystals as grown from the melt, vapour-grown crystals turn out to be better in relation to structural perfection, purity, microcompositional uniformity, growing interface stability, etc., which goes towards favouring a higher performance of various devices, in agreement with the general requirements for ever better quality single crystal materials as demanded by the electronic industry. In the frame of the above, the guest editors endeavoured to collect a number of invited contributions well able to represent the state of the art in the various aspects of vapour growth. These contributions were expected not only to highlight the latest advances and trends in the field, but also to show how techniques, theories and process modelling, targeted research on specific materials (e.g., ZnO, CdTe, SiC, GaN), have historically developed in what is today a well-funded sub-discipline of crystal growth science and technology generally. It is an added pleasure to notice that most of the contributed papers have been fully complied with these expectations. After offering high-standard reviews in the specialization areas of their authors, most of the papers are as well not devoid of a tutorial character which, for sure, will be appreciated by those growers who are not yet familiar with vapour crystal growth. This is the first of two special sectional volumes of this journal and contains five of the collected papers. The remaining papers are planned to appear in a second sectional volume within the year. The guest editors, while thanking the invited authors for their high-level reviews and excellent cooperation, would also like to express their acknowledgement for the very important role played by the Editor-in- Chief, Prof. Brian Mullin, who not only readily agreed with their suggestion on editing this journal, but also contributed in the selection of some of the review papers and, while doing a lot of the editorial work, did not spare his encouragement and useful guidance in bringing out these special volumes. The guest editors would also like to thank all the reviewers for their independent assessments and for having enabled this first volume to appear with not too much delay from the publication schedule. They are also grateful to the staff at Elsevier for their patience and professional collaboration.