Dresden 2017 – wissenschaftliches Programm
MA 24.1: Topical Talk
Dienstag, 21. März 2017, 09:30–10:00, GER 37
Synthesis of large-area single-crystal diamond by heteroepitaxy for application as dielectric window material — •Matthias Schreck, Stefan Gsell, and Martin Fischer — Institut für Physik, Universität Augsburg, 86135 Augsburg, GERMANY
Due to ist low dielectric loss tangent in combination with excellent mechanical properties and the unrivalled thermal conductivity, diamond is the optimum window material for the transmission of high power millimeter waves. Polycrystalline discs with diameters of about 100 mm synthesized by microwave plasma chemical vapor deposition (MWPCVD) are already in use as gyrotron exit windows or as injection windows for future thermonuclear fusion reactors. Since imperfections like graphitic bonds and C-H groups at grain boundaries still give rise to power absorption, the use of single crystals promises even lower loss tangents thus facilitating higher power levels. The present contribution reviews the efforts towards the synthesis of wafer-scale single-crystal diamond by heteroepitaxial growth using MWPCVD. The search for the optimum substrate material, the development of appropriate nucleation methods and the concepts for the scaling to wafer size are described. Particular attention is paid to dislocations which represent the crucial defect type. The role of dislocations in the development of intrinsic stress, the reduction of their density by growth of thick layers and by advanced deposition concepts is broadly discussed. Finally, the present state-of-the-art in terms of crystal quality and sample size is described.