Growth Mode and Defects in Aluminum Nitride Sublimed on (0001) 6H-SiC Substrates

Abstract

The effect of substrate preparation on the sublimation growth of AlN at about 1800 °C and 400 torr on (0001) 6H-SiC was investigated. The AlN grew in the step flow growth mode on an off-axis 6H-SiC substrate with a 6H-SiC epilayer, an island growth mode on as-received substrates, and a 2-D growth mode on substrates first coated with an AlN epitaxial layer by MOCVD. Cracks in the deposited AlN crystal due to the lattice and thermal expansion coefficient mismatches were always observed by SEM and optical microscopy.

Raman characterization and stress analysis of AlN grown on SiC by sublimation

“…Table I shows that the Raman peak positions are essentially the same for AlN grown on AlN buffered or as received 6H-SiC substrates at the same growth condition and growth time, although there is significant growth-mode difference for these two substrates. 10 Stress during growth appeared to be relieved by the introduced threading dislocations and was independent of the growth mode. Full width half maximums ͑FWHMs͒ of E 1 (TO) frequencies for AlN grown on as received 6H-SiC and 6H-SiC with the AlN epilayer decrease with increasing thickness, as illustrated in Fig.…”

“…10,12 Briefly, the Al and N 2 vapor created by the dissociation of the hot polycrystalline AlN source (T s ϳ1900°C) was transported to a seed held at a lower temperature (T c ϳ1800°C) in a tungsten crucible. Then adsorption/desorption took place at the surface of the growing AlN on 6H-SiC substrates leading to crystal growth.…”

“…[6][7][8][9] Previously, we have grown AlN by sublimation using a semisealed tungsten crucible in a resistively heated tungsten furnace and investigated the effect of substrate preparation on the sublimation growth of AlN at about 1800°C and 400 Torr on ͑0001͒ 6H-SiC. 10 Three problems with using 6H-SiC as the seed crystals were identified: the decomposition of SiC at high growth temperature; three-dimensional ͑3D͒ nucleation and consequent formation of individual grains in the AlN crystal; and cracking of the AlN crystal due to the thermal expansion coefficients mismatch between AlN and SiC. To circumvent the first two problems, an AlN epitaxial layer was first deposited on SiC substrates by metalorganic chemical vapor deposition ͑MOCVD͒, resulting in 2D growth mode and suppressing SiC decomposition and grain boundary formation.…”

“…To circumvent the first two problems, an AlN epitaxial layer was first deposited on SiC substrates by metalorganic chemical vapor deposition ͑MOCVD͒, resulting in 2D growth mode and suppressing SiC decomposition and grain boundary formation. 10,11 This work addresses the last problem: the stress distribution in the AlN crystals grown on SiC substrates. In this work, a theoretical model was formulated to describe the stress distribution in these AlN/6H-SiC heterostructures.…”

The initial growth stage in PVT growth of aluminum nitride

“…As a consequence of its close physical, chemical and structural nature to gallium nitride (GaN), aluminum nitride (AlN) is an excellent candidate as a III-nitride substrate material [2]. Recently, we reported on bulk AlN crystals, large enough for wafering grown by PVT technique [3].…”