Precipitates originating from tungsten crucible parts in AlN bulk crystals grown by the PVT method

• Published in: Crystal research and technology (1979) Vol. 51; no. 2; pp. 129 - 136
• Main Authors: Langhans, Frank, Kiefer, Stefan, Hartmann, Carsten, Markurt, Toni, Schulz, Tobias, Guguschev, Christo, Naumann, Martin, Kollowa, Sandro, Dittmar, Andrea, Wollweber, Jürgen, Bickermann, Matthias
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.02.2016
• Subjects: Aluminum nitride; Crucibles; Crystals; Dislocations; EPMA; precipitate; Precipitates; Precipitation; TEM; Transport; Tungsten; tungsten carbide
• ISSN: 0232-1300; 1521-4079
• DOI: 10.1002/crat.201500201

In order to evaluate the possible involvement of crucible materials in the growth of AlN bulk crystals grown by physical vapor transport, we applied growth conditions with a high vertical thermal gradient and hence high supersaturation of aluminum vapor. Under these conditions, precipitates formed causing diffuse grayish substructures at the initial growth interface and in the crystal body, decorating dislocations. Electron microscopy studies revealed that the precipitates are elongated, single‐phase particles with sizes of 50–500 nm of commensurate structure, oriented along the <112¯0> direction. Chemical analysis of the precipitates showed tungsten as well as carbon and oxygen. The lattice parameters of the precipitates are in close agreement to hexagonal tungsten hemicarbide (W2C). The possible transport from the tungsten parts and its conversion into tungsten hemicarbide precipitates is discussed. We thus conclude that the W2C precipitates may contribute to the decoration of dislocations, even in growth with moderate thermal gradients. Nanoprecipitates containing tungsten originating from the crucible parts in PVT grown AlN bulk crystals were investigated. The chemical composition and structure of the particles indicate that they consist of tungsten hemicarbide (W2C). A potential transport mechanism of tungsten over O/CO is proposed.