The growth of ultralong and highly blue luminescent gallium oxide nanowires and nanobelts, and direct horizontal nanowire growth on substrates

We report the growth of ultralong beta-Ga2O3 nanowires and nanobelts on silicon substrates using a vapor phase transport method. The growth was carried out in a tube furnace, with gallium metal serving as the gallium source. The nanowires and nanobelts can grow to lengths of hundreds of nanometers and even millimeters. Their full lengths have been captured by both scanning electron microscope (SEM) and optical images. X-ray diffraction (XRD) patterns and transmission electron microscope (TEM) images have been used to study the crystal structures of these nanowires and nanobelts. Strong blue emission from these ultralong nanostructures can be readily observed by irradiation with an ultraviolet (UV) lamp. Diffuse reflectance spectroscopy measurements gave a band gap of 4.56 eV for these nanostructures. The blue emission shows a band maximum at 470 nm. Interestingly, by annealing the silicon substrates in an oxygen atmosphere to form a thick SiO2 film, and growing Ga2O3 nanowires over the sputtered gold patterned regions, horizontal Ga2O3 nanowire growth in the non-gold-coated regions can be observed. These horizontal nanowires can grow to as long as over 10 mu m in length. Their composition has been confirmed by TEM characterization. This represents one of the first examples of direct horizontal growth of oxide nanowires on substrates.