Tailoring the shape of GaN/AlxGa1-xN nanostructures to extend their luminescence in the visible range

We show that the shape of GaN nanostructures grown by molecular beam epitaxy on AlxGa1-xN (0001) surfaces, for x >= 0.4, can be controlled via the ammonia pressure. The nanostructures are obtained from a two dimensional to three dimensional transition of a GaN layer occurring upon a growth interruption. Atomic force microscopy measurements show that depending on the ammonia pressure during the growth interruption, dot or dash-shaped nanostructures can be obtained. Low temperature photoluminescence measurements reveal a large redshift in the emission energy of the quantum dashes, as compared to the quantum dots. By simply adjusting the GaN deposited thickness, it is shown that quantum dashes enable to strongly extend the emission range of GaN/Al0.5Ga0.5N nanostructures from the violet-blue (similar to 400-470 nm) to the green-orange range (similar to 500-600 nm).