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

Abstract

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 <11true2¯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.

Preparation of deep UV transparent AlN substrates with high structural perfection for optoelectronic devices

“…However, the prismatic {10−10} facets, which cover the sides of the growing crystals, reveal much lower growth rates due to the lower supersaturation on these surfaces perpendicular to the N-polar main growth facet. In order to obtain reasonable crystal diameter enlargement, a radial temperature gradient in front of the seed is required which (i) must not be too large so that no additional defects like LAGB or basal-plane dislocations (BPD) are generated, [35][36][37] but (ii) has to be high enough to ensure appreciable growth rates on the {10−10} facets. 13,24 Furthermore, parasitic growth adjacent to the AlN single crystal must be avoided in order to increase the yield and to prevent causes of additional crystal defects by e.g.…”

Toward Φ56 mm Al-Polar AlN Single Crystals Grown by the Homoepitaxial PVT Method

“…Due to the low supersaturation of the {101̅0} surface perpendicular to the Al-polar growth plane, AlN crystals normally exhibit a low radial growth rate ( V r ). A sufficiently high radial temperature gradient (Δ T r ) around the seed surface is necessary for reasonable crystal diameter expansion, although a large Δ T r can lead to additional defects, such as low-angle grain boundaries (LAGBs) or basal plane dislocations (BPDs). − …”

Preparation of nano‐AlN powder by sol–gel foaming and its sintering properties

“…Aluminum nitride (AlN) has high thermal conductivity, high resistance, low dielectric constant, low thermal expansion coefficient, good thermal shock resistance, and corrosion resistance, [1][2][3][4] making it a hot new type of electronic ceramic that is widely used in the fields of heat dissipation packaging materials for high-power chips. [5][6][7][8][9][10] The main preparation method is carbothermal reduction method, which is limited by factors such as difficult uniform mixing of raw materials, high cost of high-temperature calcination and the need for high-purity alumina and carbon black. [11][12][13][14][15][16][17][18][19][20][21] Recently, a new type called low-temperature combination synthesis has been adopted, and the prepared AlN has a small and uniform particle size.…”