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Precipitates originating from tungsten crucible parts in AlN bulk crystals grown by the PVT method
Author(s) -
Langhans Frank,
Kiefer Stefan,
Hartmann Carsten,
Markurt Toni,
Schulz Tobias,
Guguschev Christo,
Naumann Martin,
Kollowa Sandro,
Dittmar Andrea,
Wollweber Jürgen,
Bickermann Matthias
Publication year - 2016
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.201500201
Subject(s) - tungsten , crucible (geodemography) , materials science , supersaturation , crystal growth , aluminium , crystallography , precipitation , metallurgy , chemical engineering , chemistry , computational chemistry , physics , organic chemistry , meteorology , engineering
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 <11 2 ¯ 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 (W 2 C). The possible transport from the tungsten parts and its conversion into tungsten hemicarbide precipitates is discussed. We thus conclude that the W 2 C precipitates may contribute to the decoration of dislocations, even in growth with moderate thermal gradients.