Inclined dislocation arrays in AlGaN/AlGaN quantum well structures emitting at 290 nm
Chang, T Y and Moram, M A and McAleese, C and Kappers, M J and Humphreys, C J
We report on the structural and optical properties of deep ultraviolet emitting AlGaN/AlGaN multiple quantum wells(MQWs) grown on (0001) sapphire by metal-organic vapor phase epitaxy using two different buffer layer structures, one containing a thin (1 \mum)AlN layer combined with a GaN interlayer and the other a thick (4 \mum)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 AlNsurface and terminating at bunched steps at the surface of the MQW structure. In all layers, these inclined dislocation arrays are surrounded by AlGaN with a relatively higher Ga content, consistent with plan-view cathodoluminescence maps in which the bunched surface steps are associated with longer emission wavelengths. The structure with the 4 \mum-thick AlNbuffer layer had a dislocation density lower by a factor of 2 (at (1.7±0.1)×10\^9 cm\^−2) compared to the structure with the 1 \mum thick AlNbuffer layer, despite the presence of the inclined dislocation arrays.
Department of Materials
Imperial College London
Royal School of Mines
London, SW7 2AZ - UK