Controlling Nanostructure Self-assembly for Design of Three-dimensional Semiconductor Heterostructures*

We examine the control of vertical and coaxial growth in self-assembled GaN/AlN nanowires grown on Si (111) by plasma assisted molecular beam epitaxy. To grow nanowires vertically and not radially a two-step growth method is used. Nanowires are nucleated at low temperatures and grown vertically at high temperatures, allowing for independent control of density and height and constant radius. A second method is used to promote radial growth. GaN nanowire cores are formed, then growth temperature is reduced and growth continues. Vertically and coaxially oriented AlN/GaN heterostructures grown using these methods are presented. We discuss the structural and optical properties of these GaN/AlN quantum disk and core-shell heterostructures using scanning electron microscopy, scanning transmission electron microscopy, and temperature dependent photoluminescence measurements.