Microstructures were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in order to clarify the dislocation behavior in AlGaN layers HVPE-grown on a stripe-patterned sapphire (0 0 0 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 is formed up to the top surface of thin film. When the growth from the upper side (terrace) of patterned substrate is predominant, AlGaN becomes a single-crystalline layer with a flat surface. Threading dislocations (TDs) generated from the interface to the terrace propagate upwards, inclining to the wing regions. They are scarcely merged with one another. The AlGaN layer on the patterned substrate with a wider groove has a smaller density of dislocation to be about 1 x 10(9) cm(-2). There are four types of dislocations: (1) TDs inclining toward < 1 (1) over bar 0 0 > normal to their Burgers; vector B; (2) TDs inclining toward < 2 (1) over bar (1) over bar 0 > on their slip-plane; (3) TDs inclining largely or horizontal dislocations (HDs) along < 2 (1) over bar (1) over bar 0 > and (4) roundly curved HDs lying on (0 0 0 1) plane. Some TDs change the direction of inclination, suggesting that internal stress changed intricately during the growth. (C) 2009 Elsevier B.V. All rights reserved.