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Abstract: Self-assembled high-density gallium nitride (GaN) nanorod arrays have been grown on (0001) Al2O3 substrates by metal-organic molecular beam epitaxy (MOMBE) using radio-frequency radical nitrogen. The corresponding microstructure and optical properties of nanorods were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), micro-Raman (μ-Raman) spectroscopy and temperature-dependent photoluminescence (PL). It was found that the length and diameter of nanorods varies with the growth temperatures, and the rod number density can reach around 1010 cm−2. HRTEM and corresponding diffraction patterns have revealed that the GaN nanorods have a dislocation-free, single-crystal hexagonal wurtzite structure. μ-Raman scattering reveals that the self-assembled nanorods are strain free in consistent with XRD and HRTEM results. In particular, the PL spectra show an abnormal behavior with increasing temperature. The so-called “S-shape” behavior, a red–blue–red shift of emission peak with increasing temperature, might result from the fluctuation in compositional contents or crystallographic defects. In contrast to previous works, the process requires neither catalyst nor the effect of nanometer-sized confinement such as carbon nanotubes. These strain-free GaN nanorods may find many important applications on the future development of optical nanodevices. [Copyright &y& Elsevier]

Abstract: This work reports on the heteroepitaxial growth of wurtzite indium nitride (InN) thin films on highly orientated n-ZnO buffer layer by RF metal-organic molecular beam epitaxy (RF-MOMBE) system. Highly orientated n-ZnO buffer layers were pre-sputtered using RF co-sputtering. We investigated the surface morphology and crystal structure properties by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), respectively. XRD pattern shows InN films were hexagonal wurtzite structure with preferential c-axis orientation. Electrical properties such as carrier concentration and mobility were performed by Hall measurement at room temperature. Particularly, the InN has high growth rate of 1.5μm/h. SEM images also reveal the InN surface become rough as increasing the flow rate of trimethylindium (TMI) vapor. Meanwhile, the carrier mobility decrease at higher TMI flow rate. The phenomena probably originate from surface imperfection by excess In incorporation in the films. These results indicate that the high-quality buffer layer is essential for engineering the growth of InN on silicon wafer, and it might be also applicable for other lattice-mismatched III–V heteroepitaxial systems. [Copyright &y& Elsevier]