Sublimation sandwich method

The sublimation sandwich method', sublimation sandwich process, or sublimation sandwich technique is a kind of physical vapor transport growth for creating man-made crystals. Silicon carbide is the most common crystal grown this way, though others crystals may also created with it (notably gallium nitride). In this method, the environment around a single crystal or a polycrystaline plate is filled with vapor heated to between 1600°C and 2100°C-- changes to this environment can affect the gas phase stochiometry. The source-to-crystal distance is kept between 0.02-0.03mm (very low). Parameters that can affect crystal growth include source-to-substrate distance, temperature gradient, and the presence of tantalum for gathering excess carbon. High growth rates are the result of small source-to-seed distances combined with a large heat flux onto a small amount of source material with no more than a moderate temperature difference between the substrate and the source (0.5-10°C). The growth of large boules, however, remains quite difficult using this method, and it is better suited to the creation of epitaxial films with uniform polytype structures.

Mokhov, E. et al.: “Growth of Silicon Carbide Bulk Crystals by the Sublimation Sandwich Method”, Elsevier Science S.A., 1997, pp. 317-323