The Investigation Of One-dimensional GaN And Ga₂O₃ Nanostructures Through Ammoniating The Ga₂O₃/Mo Films On Si Substrates

In this paper,GaN and Ga₂O₃ nanostructures have been synthesized on Si(111)substrates by ammoniating Ga₂O₃/Mo fihns of different middle layer thickness.Thestructure,composition,morphology and optical properties of the as-prepared GaN andGa₂O₃ nanostructures are studied thoroughly.The optical mechanism and growth mechanism of GaN and Ga₂O₃ nanostructure are firstly explored,and the influences ofdifferent growth conditions on GaN and Ga₂O₃ nanostructures are investigated also.All theresults are as follows:1. Synthesis of one-dimensional GaN nanostructuresMo middle layers and Ga₂O₃ films were deposited in turn on Si(111)substrates by aJCK-500A RF magnetron sputtering system (the deposition thickness was 30 nm for Mo layers and 500 nm for Ga₂O₃ films,respectively),and then as-grownGa₂O₃/Mo thin filmswere annealed in a conventional tube furnace under flowing ammonia to fabricate GaN nanostructure.The structure,elemental composition and morphology of the GaN nanostructures were determined by X-ray diffraction (XRD),Fourier transformed infraredspectroscopy (FTIR),X-ray photoelectron energy spectroscopy (XPS),scanning electronic microscope (SEM)and high-resolution transmission electronic microscope (HRTEM).Theresults indicate that the as-synthesized GaN nanostructures were hexagonal GaN withwurtzite structure.Different ammoniating temperature and different ammoniating time ofGa₂O₃ fihns have great influences on the synthesis of GaN nanostructure,showing theirmorphologies as nanowires and nanorods.2. Optical properties of GaN nanostructures and exploration of GaN growth mechanismFor the optical property,the measurement of PL spectrum was performed with a He-Cd laser as the excitation source (wavelength was 325 nm)at room temperature.A strongemission peak at 371.5 nm (ultraviolet band)is found.With changes of experimentalparameters,the locations of the peaks do not move,and only the intensities of them change. Because the as-prepared GaN nanostructures is too large for quantum confinement,and infact the Bohr exciton radius of GaN is 11 nm.The emission peak at 371.5 nm has no blueshift of the band-gap emission compared with the bulk GaN.The growth mechanism can be decribed as vapor-solid (VS)mechanism.Mo obtains easily oxygen from Ga₂O₃ duringthe high temperature ammoniating process,which accelerates the ammoniation of Ga₂O₃and make the energy distribution on the substrate surface to become uneven,which mayplay an important role in the formation of GaN nanostructures.3. Synthesis of one-dimensional Ga₂O₃ nanostructuresMo middle layers and Ga₂O₃ films were deposited in turn on Si(111)substrates by aJCK-500A RF magnetron sputtering system (the deposition thickness was 300 nm for Molayers and 500 nm for Ga₂O₃ films,respectively),and then as-grown Ga₂O₃/Mo thin filmswere annealed in a conventional tube furnace under flowing ammonia to fabricate Ga₂O₃nanostructure.The results show that the formed nanostructures are Ga₂O₃ with monoclinicstructure.Different annealing temperature and different annealing time of Ga₂O₃ films have great influences on the synthesis of Ga₂O₃ nanostructure,showing their morphologiesas nanowires and nanorods.4. Optical properties of Ga₂O₃ nanostructures and exploration of Ga₂O₃ growth mechanismThe measurement of PL spectrum was performed with a He-Cd laser as the excitationsource (wavelength was 325 nm)at room temperature.Two obvious blue-light peakslocated at 411.5 nm and 437.6 nm are found.The blue peaks are known to be attributed tovacancies.After excitation of the acceptor,a hole on the acceptor and an electron on thedonor are created.Then an electron on donor formed by oxygen vacancies (V_o)is captured by a hole on acceptor formed by gallium vacancies (V_Ga) to form a trapped exciton,whichrecombines to emit a blue photon.However,further work is needed to investigate the PL mechanism of theβ-Ga₂O₃ nanomaterials.A VS mechanism was still valid in the growthprocess ofβP-Ga₂O₃ nanostructures in this method.We believe the Mo particles probablyact as the nucleating sites for embryos,which lays the foundations for the growth ofnanostructuredβ-Ga₂O₃.