The initial growth stage in PVT growth of aluminum nitride

Abstract

The main issue in homoepitaxial growth of aluminum nitride (AlN) on native seed substrates is the formation of an aluminum oxynitride (AlON) layer at temperatures between 1850-1950 °C leading to polycrystalline growth. On the contrary, heteroepitaxial growth of AlN on silicon carbide (SiC) is relatively easy to achieve due to natural formation of a thin molten layer of (Al 2 OC x ) on the seed surface and consequent growth of AlN via the molten buffer layer. Optimization of the seeding process can be achieved by use of ultra-pure starting material. Another critical issue of AlN growth on SiC is cracking of the grown layer upon cooling as a result of different thermal expansion coefficients.

Initial growth stage in PVT growth of AlN on SiC substrates: Influence of Al2O3

“…In subsequent stages these compounds melt, build a liquid film and initiate vapor-liquid-solid (VLS-) growth on a refreshed seed surface (see [7] for further details). Oxygen plays a vital role in heteroepitaxial growth of AlN on SiC.…”

“…of Al 2 O 3 in relation to the weight of the AlN source disc was distributed homogeneously over the latter. In order to get a grasp on the initial growth stage, holding time at growth temperature was varied between 2-15 minutes [7], resulting in layer thicknesses up to 30 µm. The growth cell had to be cut in order to release the substrate with the grown layer.…”

“…In our arrangement dense ceramic items were machined from a bulk obtained by sintering commercially available AlN powder at temperatures between 2250-2300 °C in high-purity nitrogen atmosphere employing tungsten crucibles to decreasing oxygen content to 300 ppm. The setup is heated by a tungsten gradient heater with a source to seed distance of 2 mm (see [7] for details). Bottom and top discs separate the SiC substrate from the tungsten heaters in order to prevent the formation of tungsten carbide (WC) or tungsten silicide (WSi).…”

“…Seeded growth of AlN on SiC substrates looks very promising since high quality up to 4 inch SiC substrates are available. It was reported recently by a few groups [4][5][6][7] that heteroepitaxial seeding of AlN on SiC is easier to achieve than homoepitaxial seeding, but the reasons are still under discussion. In this paper we investigate the initial stages of seeded PVT growth of AlN on SiC.…”

Specific features of sublimation growth of bulk AlN crystals on SiC wafers

“…A pore is formed at rather low supersaturation on growing and evaporated surfaces. Presence of the liquid phase including Al, C. O and Si [11] is a possible promoter of pore formation in AlN crystals. AlN crystals grown on the SiC seeds in conditions close to optimum have a smooth surface and very small pores density (Fig.…”