A study was made of the structural and optical properties of deep ultraviolet-emitting AlGaN/AlGaN multiple quantum wells grown onto (00•1) sapphire by metal-organic vapour phase epitaxy using two different buffer layer structures, one containing a thin (1μm) AlN layer combined with a GaN interlayer and the other a thick (4μm) AlN layer. Transmission electron microscopy analysis of both structures showed inclined arrays of dislocations running through the AlGaN layers at an angle of ∼30°, originating at bunched steps at the AlN surface and terminating at bunched steps at the surface of the multiple quantum well structure. In all layers, these inclined dislocation arrays were surrounded by AlGaN with a relatively higher Ga content, consistent with plan-view cathodoluminescence maps in which the bunched surface steps were associated with longer emission wavelengths. The structure with the 4μm-thick AlN buffer layer had a dislocation density lower by a factor of 2 (at 1.7 x 109/cm2) compared to the structure with the 1μm thick AlN buffer layer, despite the presence of the inclined dislocation arrays.

Inclined Dislocation Arrays in AlGaN/AlGaN Quantum Well Structures Emitting at 290nm. T.Y.Chang, M.A.Moram, C.McAleese, M.J.Kappers, C.J.Humphreys: Journal of Applied Physics, 2010, 108[12], 123522