Abstract
The crystal structure and compositional changes near the two interfaces of a AlN/(AlN)~x~ (SiC)~1โx~ /4HโSiC heterostructure prepared by sublimationโrecondensation growth were examined by crossโsectional transmission electron microscopy. Deposition of an (AlN)~x~ (SiC)~1โx~ layer between a SiC seed and a bulk AlN crystal is potentially beneficial for gradually changing the lattice constants and coefficient of thermal expansion from SiC to AlN. A compositional transition layer adjacent to the 4HโSiC substrate suggested interdiffusion between the substrate and the alloy layer. The alloy had the 4Hโpolytype crystal structure in this layer; above the layer, the alloy exhibited the typical 2Hโpolytype. Voids were present at the AlN/(AlN)~x~ (SiC)~1โx~ interface, due to the decomposition of the (AlN)~x~ (SiC)~1โx~ layer before the AlN layer had completely coalesced. The nominally pure AlN layer contained approximately 8% of Si and C, possibly coming from the decomposition of the alloy layer and/or the substrate during growth of the AlN layer. Both interfaces were abrupt, to less than 50 nm, with low densities of threading dislocations. Dislocations in both the (AlN)~x~ (SiC)~1โx~ and AlN layers were not threading, but ran parallel to the (0001) planes. (ยฉ 2006 WILEYโVCH Verlag GmbH & Co. KGaA, Weinheim)