Thick AlGaN layers with high Al contents (50%) grown epitaxially on GaN crack

due to tensile strain arising from the lattice parameter mismatch. AlN can be used

to prevent this cracking but there was a concomitant increase in the edge-type

threading dislocations in the AlGaN film. Here, the origin of the additional

threading dislocations (TDs) was investigated. The AlN interlayer itself microcracks

to relieve strain, and overgrowth of AlGaN on such a relaxed/cracked AlN

layer gives rise to the generation of additional edge type TDs along the crack lines.

This appeared to be due to terminated misfit dislocation lines at the crack facets

that were replicated during subsequent growth, resulting in additional edge TDs in

the upper AlGaN layer. The contribution of cracks in generating additional edge

TDs can also depend on whether the crack lines were filled or a void was created

during AlGaN growth.

Origin of Additional Threading Dislocations in AlGaN Grown on GaN Using AlN

as an Interlayer. R.Datta, C.McAleese, P.Cherns, F.D.G.Rayment, C.J.Humphreys:

Physica Status Solidi C, 2008, 5[6], 1743-5