By considering the temperature differences of 50°C, this compositional

difference (i.e., indium rich in the layer in LOHN formed by VLS mechanism) is still significant that may come from the different growth mechanism [31]. The higher In composition in the VLS mechanism may be due to the precipitation of the InGaN phase from the thermodynamically supersaturated In-Ga-Ni-Au liquid phase that has a higher In/Ga ratio than the atmosphere. Our analysis shows that the composition of the metal catalyst of In-Ga-Ni-Au is ca. 20%, 10%, 20%, and 50%, respectively, when prepared under the same ratio of TMIn and TMGa in the atmosphere. This indicates that the InGaN layer in the LOHN is different from that in the COHN because it shifts to the indium-rich sides, owing to the indium-rich supersaturated PF-04929113 composition of the liquid metal catalyst. Although only one

composition is reported here, our further study shows that the composition of the InGaN layers grown by VLS mechanism via a catalyst can be controlled by the processing temperature from 0% to 50%. This indicates that the composition of the InGaN layer in LOHN can also be tuned easily by the processing temperature. Figure 4b shows the micro-PL of the individual nanowire of the GaN/In0.4Ga0.6N LOHN. A green emission can be seen at the InGaN layer with a wavelength of 520 nm. It indicates that the optical properties of the vertical MK-4827 in vitro GaN ever nanowires can be tuned by fabricating the LOHN by a VLS mechanism via bi-metal catalysts. Conclusions In summary, we have achieved the vertical growth of GaN nanowires via a VLS mechanism using Au/Ni bi-metal catalysts, which leads

to the growth of nanowires without the interfacial layer between the nanowires and the substrate and, in turn, enables their vertical growth. TEM studies have shown that the GaN nanowires are single-crystalline and dislocation-free. The vertical GaN/InGaN COHN can then be fabricated by subsequent deposition of InxGa1-xN shell onto the GaN nanowires. The vertical GaN/InGaN LOHN can also be fabricated by the subsequent growth of an InGaN layer using the catalyst. These outcomes demonstrate that bi-metal catalysts are click here versatile for the vertically aligned as well as the heterostructure GaN nanowires. Optical studies of the COHN and LOHN have demonstrated InGaN composition-dependant emission from 405 to 520 nm. Vertically aligned GaN and heterostructure nanowires (COHN, LOHN) with tunable optical properties can be expected to be useful for the fabrication of high-performance optoelectronic devices. Acknowledgements This work was supported by a grant (no. 2012R1A2A1A03010558) from the National Research Foundation of Korea (NRF) and the Pioneer Research Program for Converging Technology (2009-008-1529) of the Korea Science and Engineering Foundation, funded by the Ministry of Education, Science, and Technology, Korea.