Dislocation reduction in AlGaN grown on patterned GaN

Metalorganic vapor phase epitaxy was used to grow 15 μm of Al0.26Ga0.74N on GaN that was patterned with trenches 10 μm wide and 1 μm deep. The top of the AlGaN showed 4-μm-wide areas on either side of the trench centerline that had low threading dislocation densities, measured to be less than ∼1.5×108 cm−2. Cross-sectional transmission electron microscopy showed that in the early stages of growth, AlGaN grew at an angle from the corners of the trench and eventually coalesced over the center. These laterally propagating growth sections overgrew the vertical growth in the trench bottom, with the result that low dislocation-density areas formed at the top of the AlGaN. Detailed examination showed that the vertical dislocations from the trench bottom were bent by the angled growth toward the center of the trench where they annihilated with other dislocations, allowing the low dislocation-density areas to form above. Elemental analysis showed that the angled growth sections had slightly lower Al content. The low dislocation-density areas are sufficiently wide to permit optically emitting devices to be grown.