Role of growth temperature on formation of single crystalline GaN nanorods on flexible titanium foil by laser molecular beam epitaxy

We have studied the effect of growth temperature (550-700 degrees C) on the morphological, structural and optical properties of GaN nanostructures grown directly on flexible Ti metal foil by laser assisted molecular beam epitaxy (LMBE). The low growth temperature (550 degrees C) favors a growth of dense, three-dimensional GaN islands whereas probe-shaped sparse GaN nanorods (NRs) are obtained at 700 degrees C. The average length, diameter and density of GaN NRs were analyzed from field emission scanning electron microscopy images and were estimated to be 80 nm, 260 nm and similar to 9.6 x 10(8) cm(-2) respectively. The high-resolution transmission electron microscopy analysis confirmed that the GaN NRs have single crystalline structure over the entire length and had grown along c-axis. Raman spectroscopy studies revealed that the LMBE grown GaN nanostructures on Ti foil possess wurtzite structure with a low tensile stress (0.15-0.37 GPa). The intense near band edge emission peak appeared at 3.42 eV, similar to bulk GaN, with a smaller full width at half maximum of 100 meV for the sparse GaN NRs grown at 700 degrees C. Direct growth of GaN NRs at a relatively lower temperature on flexible metal foils with high structural and optical quality holds the promise for the fabrication of flexible GaN based futuristic optoelectronics devices.