Interface properties of an AlN/(AlN)_x(SiC)_(1-x)/4H-SiC heterostructure

摘要

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.