TEM Study of Defects in Laterally Overgrown GaN Layers

Transmission electron microscopy was applied to study defects in laterally overgrown GaN layers, with initial growth on A1 2 O 3 substrates followed by further growth over SiO 2 masks. Dislocations found in the overgrown areas show changes in line direction. Most dislocations propagate along c-planes. In the overgrown material planar defects (faulted loops) are present on c-planes and their presence is most probably related to segregation of excess point defects and impurities present in this material. They appear to be initiated by the fast lateral growth. Some dislocations with screw orientation become helical resulting from climb motion. Formation of voids and also a high dislocation density was observed at the boundaries where two overgrowing fronts meet. Tilt and twist components were observed for these boundaries that were different for different overgrown strips grown in the same crystallographic direction suggesting that the GaN subgrain orientations on the two sides of a SiO 2 mask are responsible for the final tilt and twist value.