Synthesis of GaN nanowires by CVD method: effect of reaction temperature

GaN nanowires are fabricated on Si substrates by ammoniating Ga₂O₃/NiCl₂ thin films using chemical vapour deposition method. The influence of reaction temperature on microstructure, morphology and optical properties of GaN nanowires is characterised by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrophotometer, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The results demonstrate that the GaN nanowires are single crystalline and exhibit hexagonal wurtzite symmetry. The best crystalline quality was achieved for an reaction temperature of 1150°C for 15?min. The growth process follows vapour–liquid–solid mechanism and Ni plays an important role as the nucleation point and as a catalyst.     

Fabrication of GaN nanowires on Pd-coated sapphire substrates by magnetron sputtering technique

Large-scale GaN nanowires were successfully synthesized through ammoniating Ga₂O₃/Pd films sputtered on the sapphire(001) substrates. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence and Raman spectrum were used to characterize the specimens. The results demonstrate that nanowires are single crystal with hexagonal wurtzite structure and have good optical properties. Raman scattering appears broadened and asymmetric compared with those of bulk GaN due to its polycrystalline nature. In addition, the growth mechanism of GaN nanowires is briefly discussed.     

Synthesies and properties of Tb-doped GaN nanowires

The synthesis of Tb-doped GaN nanowires on Si (111) substrates through ammoniating Ga₂O₃ films doped with Tb was investigated. X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and photoluminescence were used to characterize the composition, structure, morphology and optical properties of the products. The results show that the as-synthesized GaN nanowires doped with 3 at % Tb are of single-crystalline hexagonal wurtzite structure. The nanowires have diameters ranging from 30 to 50 nm and the lengths up to tens of micrometers. An f-f intra-atomic transition of rare earth at 545 nm corresponding to ⁵ D ₄–⁷ F ₅ of the Tb³⁺ and other two peaks related with doping are observed in PL spectrum, confirming the doping of Tb into GaN. The growth mechanism of GaN nanowires was discussed briefly.     

Fabrication and structure properties of GaN nanowires by ammoniating Ga2O3 films

The GaN nanowires were successfully synthesized on Si(111) substrates by ammoniating the Ga₂O₃/ZnO films at 900 °C. The structure and morphology of the as-prepared GaN nanowires were studied by X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM) and field-emission transmission electron microscopy (FETEM). The results show that the single-crystal GaN nanowires have a hexagonal wurtzite structure with lengths of about several micrometers and diameters ranging from 30 nm to 120 nm, which are conducive to the application of nanodevices. Finally, the growth mechanism is also briefly discussed.     

Catalytic synthesis of large-scale GaN nanorods

A novel rare earth metal seed was employed as the catalyst for the growth of GaN nanorods. Large-scale GaN nanorods were synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(1 1 1) substrates. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy were used to characterize the structure, morphology, and composition of the samples. The results demonstrate that the nanorods are high-quality single-crystal GaN with hexagonal wurtzite structure. The growth mechanism of GaN nanorods is also discussed.     

Effect of ammoniating temperature on microstructure of one-dimensional GaN nanorods with Tb intermediate layer

GaN nanorods have been successfully synthesized on Si (111) substrates by magnetron sputtering through ammoniating Ga₂O₃/Tb thin films. The influence of ammonating temperatures on microstructure, morphology and light emitting properties of GaN nanorods was ananlyzed in detail using X-ray diffraction, X-ray photoelectron spectroscopy, FT-IR spectrophotometer, scanning electron microscopy, high- resolution transmission electron microscopy, and photoluminescence spectroscopy. The results demonstrate that the GaN nanorods are single crystalline and exhibit hexagonal wurtzite symmetry. The highest crystalline quality was achieved at 950 °C for 15 min with the size of 100–150 nm in diameter, which have an excellent light emitting properties. A small red-shift occurs due to band-gap change caused by the tensile stress.     

Fabrication of single-crystalline gallium nitride nanowires by using alginate as template

Hexagonal gallium nitride nanowires were synthesized successfully by solvothermal method with alginate as template. The microstructure, morphologies and compositions of the as-prepared product were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray (EDX). Results suggested that the rod-like nanowires were hexagonal single-crystalline GaN growing along [001] direction. The photoluminescence spectra (PL) of the GaN revealed that the as-synthesized sample possesses excellent optical properties.     

Synthesis of GaN nanowires through Ga2O3 films' reaction with ammonia

GaN nanowires were synthesized by ammoniating Ga₂O₃ films on Ti layers deposited on Si (111) substrates at 950 °C. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM). The XRD, FTIR and HRTEM studies showed that these nanowires were hexagonal GaN single crystals. SEM observation demonstrated that these GaN nanorods with diameters ranging from 50 nm to 100 nm and lengths up to several micrometers intervene with each other on the substrate.     

Fabrication of GaN nanowires and nanorods catalyzed with tantalum

Single-crystalline GaN nanowires and nanorods have been fabricated through ammoniating Ga₂O₃ films catalyzed with tantalum (Ta) by RF magnetron sputtering, and microstructure, morphology and optical properties were investigated in particular. The results indicate that the nanowires have a hexagonal wurtzite structure with size about 50 nm in diameter and more than ten microns in length, however, the nanorods are rod-like structures with smooth surface and 100–300 nm in diameter. The growth direction of these nanostructures are perpendicular to the (100) crystal plane. The photoluminescence spectrum at room temperature exhibits a strong UV light emission band centered at 364 nm.     

Effect of ammoniating temperature on morphologic and optical properties of GaN nanostructured materials

GaN nanostructured materials have been obtained on Si(111) substrates by ammoniating the Ga₂O₃/ZnO films at different temperature in a quartz tube. X-ray diffraction (XRD), Scanning electron microscope (SEM), and photoluminescence (PL) are used to analyze the structure, morphology and optical properties of GaN nanostructured films. The results show that their properties are investigated particularly as a function of ammoniating temperature. The optimally ammoniating temperature of Ga₂O₃ layer is 950 °C for the growth of GaN nanorods. These nanorods are pure hexagonal GaN wurtzite structure with lengths of about several micrometers and diameters of about 200 nm, which is conducive to the application of nanodevices. Finally, the growth mechanism is also briefly discussed.     

Fabrication of needle-shaped GaN nanowires by ammoniating Ga2O3 films on MgO layers deposited on Si (111) substrates

Needle-shaped GaN nanowires have been synthesized on Si (111) substrate through ammoniating Ga₂O₃/MgO films under flowing ammonia atmosphere at the temperature of 950 °C. The as-synthesized GaN nanowires were characterized by X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The results demonstrate that these nanowires are hexagonal GaN and possess a smooth surface with an average diameter about 200 nm and a length ranging from 5 μm to 15 μm. In addition, the diameters of these nanowires diminish gradually. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

Gallium nitride nanowires doped with magnesium

GaN nanowires doped with Mg have been synthesized on Si (111) substrate through ammoniating Ga₂O₃ films doped with Mg under flowing ammonia atmosphere. The Mg-doped GaN nanowires were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL). The results demonstrate that the nanowires were single crystalline with hexagonal wurzite structure. The diameters of the nanowires ranged 20-30 nm and the lengths were about hundreds of micrometers. The intense PL peak at 359 nm showed a blueshift from the bulk band gap emission, attributed to Burstein-Moss effect. The growth mechanism of the crystalline GaN nanowires is discussed briefly.     

Influence of reaction time on growth of GaN nanowires fabricated by CVD method

GaN nanowires have been fabricated successfully on Si (111) substrates coated with NiCl₂ thin films by chemical vapor deposition method using Ga₂O₃ as raw material. The growth of GaN nanowires was investigated as a function of reaction times so as to study the influence of different durations on the components, microstructure, morphologies and optical properties of GaN samples in particular by X-ray diffraction, FT-IR spectrophotometer, scanning electron microscope, and photoluminescence. The results show that the samples after reaction are single crystal GaN with hexagonal wurtzite structure and high-quality crystalline after reaction at 1,100 °C for 60 min, which have good optical properties as revealed by PL spectra. Reaction time greatly influences the growth of GaN nanowires, that is, with the increase in reaction time, the crystalline quality of GaN nanowires is improved accordingly. The growth of the GaN nanowires follows the vapor–liquid-solid mechanism and Ni plays an important role as catalyst, which forms nucleation point in the growth of GaN nanowires.     

Synthesis of single-crystal GaN nanowires on Si(111) substrate by ammonification technology

GaN nanowires have been synthesized on Si(111) substrate through ammoniating Ga₂O₃/BN films under flowing ammonia atmosphere at the temperature of 900 °C. The as-synthesized GaN nanowires were characterized by X-ray diffraction (XRD), selected-area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results demonstrated that the nanowires are hexagonal wurtzite GaN and possess a smooth surface with diameters ranging from 40 to 100 nm and lengths up to several tens of micrometers. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

Control of growth orientation and shape for epitaxially grown In2O3 nanowires on a-plane sapphire

Vertically aligned indium oxide nanowires were grown on a-plane sapphire substrate by the method of catalyst-assisted carbothermal reduction. The morphology and crystal structure of the nanowires are determined by X-ray diffraction, transmission electron microscopy and field-emission scanning electron microscopy. Two types of In₂O₃ nanowires were found by controlling the growth conditions. The nanowires with a hexagonal cross-section were shown to grow in [1 1 1] direction, whereas those with a square cross-section grow in [0 0 1] direction. In addition to the temperature effects, the concept of supersaturation in Au catalyst is proposed to explain the formation of these two types of nanowires. Besides, tapering, which is explained with the interplay between the vapor-liquid-solid and vapor-solid growth mechanisms, is observed in the nanowires.     

Synthesis of GaN nanorods by ammoniating Ga2O3 films on TiO2 (rutile) layer deposited on Si(111) substrates

GaN nanorods have been synthesized by ammoniating Ga₂O₃ films on a TiO₂ middle layer deposited on Si(111) substrates. The products were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectra (FTIR) and high-resolution transmission electron microscopy (HRTEM). The XRD analysis indicates that the crystallization of GaN film fabricated on TiO₂ middle layer is rather excellent. The FTIR, SEM and HRTEM demonstrate that these nanorods are hexagonal GaN and possess a rough morphology with a diameter ranging from 200 nm to 500 nm and a length less than 10 μm, the growth mechanism of crystalline GaN nanorods is discussed briefly.     

Self-organized formation and optical study of GaN micropyramids

In this paper, we report the formation of GaN micropyramids via a self-organized process by ammoniating Ga₂O₃ powders at high temperature. The obtained GaN micropyramids are typically in wurtzite hexagonal structure, exhibiting six-fold symmetrical morphology and single crystalline characteristic. Cathodoluminescence (CL) studies demonstrated that a weak near-band-edge emission centered at ∼385 nm and a broad yellow-band in the range of 500-800 nm were observed in the GaN micropyramids, and the related light emission mechanism was discussed based on the microstructure analysis.     

Synthesis of radial-aligned GaN nanorods by ammoniating Ga2O3 films on Mg layer deposited on Si(111) substrates

Radial-aligned GaN nanorods were synthesized by ammoniating Ga₂O₃ films on Mg layer deposited on Si(111) substrates. The products were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectra (FTIR) and high-resolution transmission electron microscopy (HRTEM). The SEM images indicated that the products consisted of radial-aligned GaN nanorods. The XRD and the selective area electron diffraction (SAED) patterns showed that nanorods were hexagonal GaN single crystals.     

Synthesis and optical properties of single-crystalline GaN nanorods

Single-crystalline GaN nanorods were successfully synthesized on Si(1 1 1) substrates through ammoniating Ga₂O₃/Mo films deposited on the Si(1 1 1) substrate by radio frequency magnetron sputtering technique. The as-synthesized nanorods are confirmed as single-crystalline GaN with wurtzite structure by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Scanning electron microscopy (SEM) displays that the GaN nanorods are straight and smooth with diameters in the range of 100-200 nm and lengths typically up to several micrometers. X-ray photoelectron spectroscopy (XPS) confirms the formation of bonding between Ga and N. The representative photoluminescence spectrum at room temperature exhibits a strong and broad emission band centered at 371.1 nm, attributed to GaN band-edge emission. The growth process of GaN nanorod may be dominated by vapor-solid (VS) mechanism.     

Growth and properties of vertically well-aligned GaN nanowires by thermal chemical vapor deposition process

The vertically well-aligned GaN nanowires on c-Al₂O₃ substrates were grown via a vapor-liquid-solid mechanism. X-ray diffraction indicated the GaN nanowires to have epitaxial and homogeneous in-plan alignment with the c-Al₂O₃ substrates and a strong preferred orientation along the c-axis. The GaN nanowires had a single-crystalline hexagonal structure and c-axis orientation, as confirmed by high resolution transmission electron microscopy.