Controlled 1-D to 3-D growth mode transition of GaN nanostructures and their optical properties

GaN nanostructures with high degree of growth mode control in a simple chemical vapor deposition (CVD) system are reported. The shape of nanostructures can be varied from 1-D nanowire to a 3-D polyhedron depending on the growth conditions. A systematic control over the growth parameters leads to growth mode transition from 1-D to 3-D GaN nanostructures. At higher temperatures the nanostructure shapes and polarity were dependent on the growth substrate also. Polyhedrons with Ga-face was observed on silicon, whereas pyramid-like nanostructures with N-face were observed on GaN and AlN substrates. The room temperature optical properties correlate well with the growth mechanism as characterized by cathodoluminescence spectroscopy. Polyhedrons show intense red luminescence and nanowires show intense yellow luminescence, which are attributed to N-vacancy and Ga-vacancy related defect complexes, respectively. These results on the comprehensive shape control with systematic parametric study and correlation with the optical properties are first of its kind in literature, which will be useful for the fabrication of GaN nano-photonic devices.