Observation of vertical honeycomb structure in InAlN/GaN heterostructures due to lateral phase separation

The microstructure of InxAl1-xN/GaN heterostructures (where x similar to 0.13-0.19), grown by molecular beam epitaxy, was investigated by transmission electron microscopy. Observations in the cross-section and plan-view geometries show evidence for lateral phase separation originating at the GaN surface that results in a vertical honeycomblike structure within the InAlN layers. The lateral dimensions of the honeycomb cells are similar to 5-10 nm. The vertical walls are In rich with a width of similar to 1-2 nm and align roughly perpendicular to < 11 (2) over bar0 > and < 1 (1) over bar 00 > directions. The phase separation is attributed to random compositional fluctuations during the early stages of growth, possibly associated with misfit-strain relaxation. (c) 2007 American Institute of Physics.