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Special Issue "Advances in Epitaxial Materials"
A special issue of Materials (ISSN 1996-1944).
Deadline for manuscript submissions: closed (31 July 2019).
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate. The term epitaxy comes from the Greek roots “epi” (ἐπί), meaning "above", and “taxis” (τάξις), meaning "an ordered manner". For most technological applications, it is desired that the deposited material form a crystalline overlayer that has one well-defined orientation with respect to the substrate crystal structure (single-domain epitaxy).
At one extreme, we deal with homoepitaxy on perfect substrates, for example Si epitaxial layers on Si substrates. However, even in such cases, the properties (related to the presence of point defects) of the layer depend on growth parameters: Substrate off-orientation, growth rate, pressure, or temperature.
At the second extreme, we deal with polycrystalline layers on polycrystalline substrates. In that case, we have different epitaxy relation on each crystallite. Such case can happen in the technology of metal contacts and resistivity of these contacts can depend on epitaxial relations of the junction.
The most frequent case is somewhere between those two extrema. A good example is the growth of GaN layers on sapphire. In that case, the lattice mismatch is large (16%) and must be relaxed by a high density of misfit dislocations. However, for the useful optoelectronic devices (for example, blue LEDs for white lighting), it is necessary to have much lower density of dislocations. To achieve that, a number of technological tricks are used to filter dislocations, as low temperature buffer layers, strained interlayers, lateral epitaxy, and some others.
In heteroepitaxy, the basic information needed is on the critical thickness and strain for lattice relaxation by emission of dislocations, cracking or three-dimensional growth. However, these critical thickness and strain depend on several other parameters, for example, on density of dislocations in the substrate, point defect density in the layer, or growth temperature. This makes the problems of epitaxy fascinating, but, at the same time, very difficult to study.
Moreover, in epitaxy, we deal not only with complicated mechanisms of epitaxial growth, but also features specific for a reactor. For example, in nitride technology, it is not uncommon to switch-off the flow of TEGa, but the GaN is still growing. Additionally, the inhomegeneities of the epi-wafers are observed in nano-, micro-, and even mili-scales. This makes analysis of the wafers very laborious, and, unfortunately, very often done not thoroughly enough.
Future electronic and optoelectronic devices will be based not only on two-dimensional epi-wafers, but using lateral patterning, more sophisticated three-dimensional objects (quantum dots, wires) can be grown. This is a big challange as the growth conditions are very much different in that case, and the characterization of such structures is much more difficult.
All those and other issues of epitaxy will be dealt in this Special Issue. It is my pleasure to invite you to submit a manuscript for it. Full papers, communications, and reviews are all welcome.Prof. Mike Leszczynski
Manuscript Submission Information
Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.
Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.
Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.
- lattice mismatch
- lattice relaxation
- misfit dislocations