Interface properties of an AlN/(AlN) x (SiC) 1– x /4H‐SiC heterostructure

The crystal structure and compositional changes near the two interfaces of a AlN/(AlN) x (SiC) 1– x /4H‐SiC heterostructure prepared by sublimation‐recondensation growth were examined by cross‐sectional transmission electron microscopy. Deposition of an (AlN) x (SiC) 1– x 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 4H‐SiC substrate suggested interdiffusion between the substrate and the alloy layer. The alloy had the 4H‐polytype crystal structure in this layer; above the layer, the alloy exhibited the typical 2H‐polytype. Voids were present at the AlN/(AlN) x (SiC) 1– x interface, due to the decomposition of the (AlN) x (SiC) 1– x 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) 1– x and AlN layers were not threading, but ran parallel to the (0001) planes. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)