Vertically Aligned (In)GaN Nanowires Grown by MOCVD.

Wide-bandgap, nitride-based semiconductors have gained a lot of attention for optoelectronic devices (e.g. photovoltaics (PVs), light emitting diodes (LEDs), and laser diodes (LDs)) thanks to their remarkable material properties. However, due to lattice mismatch, most epitaxially grown InGaN-based devices are limited by the quality of the GaN layer and the total thickness of the InGaN layers that can be stacked on the substrate. These challenges seriously affect our ability to produce high performance optoelectronic devices. The unique growth mechanism of nanowires can circumvent these issues by effectively relaxing the strain on lattice-mismatched substrate, thus allowing the growth of defect- and strain-free materials. First, we report the growth of a-plane GaN thin film on top of GaN nanowires by metal organic chemical vapor deposition (MOCVD). We analyzed the microstructural properties and the results showed that small-angle tilts and twists of the nanowires were the primary causes of defects in the top GaN films. To this end, we have developed a novel multi-stage growth process for coalesced nanowires to further improve the a-plane GaN film quality. Furthermore, defect-free vertically aligned bulk InGaN nanowires were achieved by MOCVD for the first time. The Indium composition in the InGaN alloy can be continuously tuned from 0 to 19%, covering the blue and green part of the visible spectrum. Because of the significance of these wavelengths, our work has the potential to not only impact high power LEDs and LDs device but also enable efficient energy conversion in PVs applications.