Growth Mechanism, Structure Regulation And Properties Of One-Dimensional Nanostructures

As known, the family of groupⅢnitrides including AlN, GaN, InN and their alloys have been recognized as the important wide bandgap semiconductor materials due to their successful applications in (opto)electronic devices. With the development of nanotechnology, their one-dimensional (1D) nanostructures have attracted increasing attention for the potential applications in nanodevices and basic research interests. In this dissertation, we focused on the studies about the growth mechanism, structure regulation and properties of 1D nanostructures of group III nitrides. Some new results have been obtained, which are briefly summarized as follows:1. Phase-Equilibrium-Dominated Vapor-Liquid-Solid Growth MechanismVapor-liquid-solid (VLS) growth model has been widely used to direct the growth of 1D nanomaterials, but the origin of the proposed process has not been experimentally convinced. Here we report the experimental evidence on the origin of VLS growth. Al69Ni31 alloyed particles are used as'catalyst' for growing AlN nanowires by nitridation reaction in N2-NH3 at different temperatures. The nanowire growth occurs following the emergence of the'catalyst'droplets as revealed by in situ X-ray diffraction and thermal analysis. The physicochemical process involved has been elucidated by quantitative analysis on the evolution of the lattice parameters and relative contents of the nitridation products. These direct experimental results reveal that VLS growth of AlN nanowires is dominated by the phase equilibrium of Al-Ni alloy'catalyst'. The in-depth insight into VLS mechanism indicates the general validity of this growth model, and may facilitate the rational design and controllable growth of 1D nanomaterials according to the corresponding phase diagrams.2.Growth and Characterization of Ternary AlGaN Alloy Nanocones across the Entire Composition RangeAlGaN ternary alloys have unique properties suitable for numerous applications due to their tunable direct bandgap from 3.4 to 6.2 eV by changing the composition. Herein we report a convenient vapor-solid growth of the quasi-aligned AlxGa1-xN alloy nanocones over the entire composition range.The nanocones were grown on Si substrates in large area by the reactions between GaCl3, AlCl3 vapors and NH3 gas under moderate temperature around 700℃.The as-prepared wurtzite AlxGa1-xN nanocones have single crystalline structure preferentially growing along the c-axis, with homogeneous composition distribution, as revealed by the characterizations of electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and selected area electron diffraction. The continuous composition tunability is also demonstrated by the progressive evolutions of the bandedge emission in cathodoluminescence,and the turn-on and threshold fields in field emission measurements.The successful preparation of AlxGa1-xN nanocones provides the new possibility for the further development of advanced nano-and opto-electronic devices.Group-Ⅲnitride semiconductors have a pronounced piezoelectric property owing to their wurtzite crystal structures.In terms of the coupling between their piezoelectric and semiconducting properties, an output power should be generated by scanning an atomic force microscope tip in contact mode across 1D group-Ⅲnitride nanomaterials. In this study, a family of 1D group-Ⅲnitrides, including AlN and AlGaN nanocones, GaN nanorods and InN nanocones, are synthesized through a facile chemical-vapor-deposition route based on previous work. Increasing electricity generation is demonstrated following the sequence:AlN, AlGaN, GaN and InN, which can be attributed to the increasing piezoelectric potential and carrier density. These results not only extend piezotronics to a new domain of group-Ⅲnitrides, but also deepen the understanding of the underlying physics of piezoelectric nanogenerators.3. Synthesis and Characterization of Mn (Eu, In)-Doped AlN NanoconesAs one of the importantⅢ-Ⅴsemiconductors, AlN has many attractive physical properties and plays an important role in the microelectronics industry.1D nonostructures of AlN have promising applications in field emission, optoelectronic devices,and so on. However, the wide bandgap and low conductivity of AlN restricts its wide applications. Dopant is an effective method to adjust the optical, electrical, magnetic and transport properties of the semiconductor materials. Using AlCl3, MnCl2 and NH3 as Al,Mn and N sources respectively, Mn-doped AlN nanocones were synthesized on Si substrates by a convenient vapor-solid growth process.Using the similar method, Eu (In)-Doped AlN nanocones can be obtained by introducing of anhydrous EuCl3 (InCl3) as the Eu (In) source. The obtained products were characterized and the properties of Mn-doped AlN nanocones were studies, the results show that the Mn (Eu, In)-doped AlN nanocones were successful synthesized.