Growth and luminescence properties of InN nanobelts (InNNBs) and InGaN nanowires (NWs) by MOCVD and thermal
CVD will be presented, along with their relation and difference to thin film counterparts. While there is a growing
acceptance of the low band gap (0.6-0.7 eV) of InN, the optical properties of the actual samples still suffered,
presumably due to the difficulty in obtaining high-quality samples and/or controlling their defect and carrier
concentrations. However, the free-standing nanobelts can be nearly defect-free, allowing an excellent opportunity for
fundamental investigations on unique dimensionality. InNNBs show photoluminescence (PL) in IR with peak width of
14 meV, the sharpest reported to date for InN. Interestingly, with increasing excitation intensity, InNNBs reveal an
anomalously large blueshift in PL, compared to thin films; along with a decrease in the phonon frequencies as evident by
Raman measurements. Surface band bending, converse piezoelectric effect, and photoelastic effects are employed to
explain these behaviors. As for InGaN NWs, both In-rich and Ga-rich ternary nanowires have been synthesized by
simply varying growth temperature. Morphological and structural characterizations reveal a phase-separated
microstructure wherein the isovalent heteroatoms are self-aggregated, forming self assembled quantum dots (SAQDs)
embedded in NWs. The SAQDs are observed to dominate the emission behavior of both In-rich and Ga-rich nanowires,
which has been explained by proposing a multi-level band schema.
Vertical hexagonal GaN nanorods are grown on (111)Si substrates by plasma-assisted molecular beam epitaxy. No extra catalyst is used to assist the GaN nanorods growth. Nanorods top surfaces are hexagons with diameter ≤10-200 nm by field emission scanning electron microscopy. The image of high-resolution transmission electron microscopy (HR-TEM) shows that the nanorods are single crystal without dislocations. Diffraction pattern of TEM also shows that the nanorods are wurtzite GaN with direction  along the length direction. The temperature dependent photoluminescence (PL) spectroscopy shows only one peak at 3.405 eV at room temperature but two peaks at 3.467 eV and 3.433 eV at 66 K. After ammonia sulfur [(NH4)2S] treatment, the low energy peak disappears. The PL spectra are also compared to the ones of epitaxial GaN thin film on (111)Si and it concludes that the low energy peak is from the nanorods contribution. The micro-Raman spectroscopy shows Stokes scattering lines at 532.7 cm-1, 558.3 cm-1, 567.1 cm-1, and 736.1 cm-1 with 532 nm laser focused on the rod lateral surface and at 558.7 cm-1, 567.8 cm-1, and 736.4 cm-1 focused on the film from the top. The width and the length of the nanorods vary with the growth time and the nanorods growth rate keeps ~20 % higher than the film. The growth mechanisms will be discussed.