Microstructures were investigated by transmission electron microscopy and scanning electron microscopy in order to clarify the dislocation behaviour in AlGaN layers HVPE-grown on a stripe-patterned sapphire (00•1) substrate. SEM observation revealed very clearly the growth process: if AlGaN starting to grow from the side-wall of patterned substrate develops, a poly-crystalline region was formed up to the top surface of thin film. When the growth from the upper side (terrace) of patterned substrate was predominant, AlGaN became a single-crystalline layer with a flat surface. Threading dislocations generated from the interface to the terrace propagate upwards, inclining to the wing regions. They were scarcely merged with one another. The AlGaN layer on the patterned substrate with a wider groove had a smaller density of dislocation to be about 109/cm2. There were four types of dislocations: (1) threading dislocations inclining toward <1¯1•0> normal to their Burgers vector B; (2) threading dislocations inclining toward <2¯1•0> on their slip-plane; (3) threading dislocations inclining largely or horizontal dislocations along <2¯1•0> and (4) roundly curved horizontal dislocations lying on (00•1) planes. Some threading dislocations changed the direction of inclination, suggesting that the internal stresses changed during growth.

Electron Microscopy Analysis of Dislocation Behavior in HVPE-AlGaN Layer Grown on a Stripe-Patterned (0001) Sapphire Substrate. N.Kuwano, Y.Kugiyama, Y.Nishikouri, T.Sato, A.Usui: Journal of Crystal Growth, 2009, 311[10], 3085-8