Synthesis and photoluminescence of single-crystal GaN nanorods prepared by sol-gel method

A new method was applied to prepare GaN nanorods. In this method, gallium oxide (Ga₂O₃) gel was firstly formed by a sol-gel processing using gallium ethanol, Ga(OC₂H₅)₃, as a new precursor. GaN nanorods were successfully synthesized after annealing of the Ga₂O₃ gel at 1000 °C for 20 min in flowing ammonia. The as-prepared nanorods were 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). Transmission electron microscopy (TEM) displayed that the GaN nanorods were straight and smooth, with diameters ranging from 200 nm to 1.8 μm and lengths typically up to several tens of microns. When excited by 280 nm light at room temperature, the GaN nanorods had a strong ultraviolet luminescence peak located at 369 nm and a blue luminescence peak located at 462 nm, attributed to GaN band-edge emission and the existence of the defects or surface states, respectively.     

Fabrication,morphology and optical properties of GaN nanorods by ammoniating Ga2O3/Nb films

Wurtzite GaN nanorods have been successfully synthesized on Si(111) substrates through ammoniating Ga₂O₃/Nb films under flowing ammonia atmosphere at 950 ^°C in a quartz tube. The nanorods have been confirmed as hexagonal wurtzite GaN by X-ray diffraction (XRD) and selected-area electron diffraction (SAED). Scanning electron microscopy (SEM) and field-emission transmission electron microscope (FETEM) reveal that the nanorods are straight and uniform, with a diameter of ranging from 100 to 200 nm and lengths up to several microns. The photoluminescence spectra (PL) measured at room temperature only exhibit a strong emission peak at 368.5 nm. Finally, the growth mechanism of GaN nanorods is also briefly discussed.     

Two-step synthesis of one-dimensional single crystalline GaN nanowires

Straight and smooth GaN nanowires were synthesized on quartz substrates through the direct reaction of Ga₂O₃ thin films with flowing ammonia in a horizontal oven without using a template or catalyst. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM) and photoluminescence (PL) were used to characterize the samples. The straight and smooth cylindrical nanostructures are high quality single crystalline hexagonal wurtzite GaN nanowires with diameters ranging from 5 to 30 nm and lengths up to 20 μm. The near-band-edge emission peak located at 367 nm was observed at room temperature.     

Growth and characterization of pine-needle-shaped GaN nanorods by sputtering and ammoniating process

Pine-needle-shaped GaN nanorods have been successfully synthesized on Si(111) substrates by ammoniating Ga₂O₃/Nb films at 950 ^°C in a quartz tube. The products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and field-emission transmission electron microscope (FETEM). The results show that the pine-needle-shaped nanorods have a pure hexagonal GaN wurtzite with a diameter ranging from 100 to 200 nm and a length up to several microns. The photoluminescence spectra (PL) measured at room temperature only exhibit a strong emission peak at 368 nm. Finally, the growth mechanism of GaN nanorods is also briefly explored.     

Growth of β-Ga2O3 nanobelts on Ir-coated substrates

We demonstrate the production of gallium oxide (Ga₂O₃) nanobelts on iridium (Ir)-coated substrates by thermal evaporation of GaN powders. Scanning electron microscopy revealed that the product consisted of nanobelts with widths in the range of 100–700 nm and thicknesses less than 1/5 of the widths. X-ray diffraction and high-resolution transmission electron microscopy indicated that the nanobelts have the single-crystalline monoclinic structure of Ga₂O₃. The photoluminescence spectrum under excitation at 325 nm showed a broad band with a prominent emission peak around 433 nm.PACS 81.07.-b     

Synthesis of GaN nanowires by Tb catalysis

Rare earth metal seed Tb was employed as catalyst for the growth of GaN wires. GaN nanowires were synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(1 1 1) substrates. The samples characterization by X-ray diffraction and Fourier transform infrared indicated that the nanowires are constituted of hexagonal wurtzite GaN. Scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy showed that the samples are single-crystal GaN nanowire structures. The growth mechanism of the GaN nanowires is discussed.     

Growth and characterization of GaN nanorods through ammoniating process by magnetron sputtering on Si(111) substrates

GaN nanorods have been successfully synthesized on Si(111) substrates by magnetron sputtering through ammoniating Ga₂O₃/ZnO films at 950 °C in a quartz tube. The GaN nanorods are characterized by X-ray diffraction, scanning electron microscopy, field-emission transmission electron microscopy, X-ray photoelectron spectroscopy and fluorescence spectrophotometry. The results show that the nanorods have a pure hexagonal GaN wurtzite structure with lengths of about several micrometers and diameters of about 200 nm, and the growth direction of the GaN nanorods is parallel to the (101) plane. The photoluminescence spectrum indicates that the nanorods have a good emission property. Finally, the growth mechanism is also briefly discussed. PACS 61.46.+w; 78.55.Cr; 81.15.Cd; 81.07.-b; 82.30.Hk     

Synthesis and characterization of GaN nanowires by ammoniating Ga2O3/Cr thin films deposited on Si(1 1 1) substrates

GaN nanowires have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/Cr thin films at 950 °C. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrophotometer, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and photoluminescence (PL) spectrum were carried out to characterize the microstructure, morphology, and optical properties of GaN samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high-quality crystalline, have the size of 30-80 nm in diameter and several tens of microns in length with good emission properties. The growth direction of GaN nanowires is perpendicular to the fringe of (1 0 1) plane. The growth mechanism of GaN nanowires is also discussed in detail.     

Synthesis of single crystalline GaN nanoribbons on sapphire (0001) substrates

Single crystalline GaN nanoribbons were synthesized through nitriding Ga₂O₃ thin films deposited on sapphire (0001) substrates by radio frequency magnetron sputtering. The component and structure of nanoribbons were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The flat and smooth ribbon-like nanostructures are high quality single crystalline hexagonal wurtzite GaN. The thickness and width-to-thickness ratio of the grown GaN nanoribbons are in the range of 8-15 nm and ∼5-10, respectively.     

Fabrication, morphology, and photoluminescence properties of GaN nanowires and nanorods by ammoniating Ga2O3/V films on Si(1 1 1)

GaN nanowires and nanorods have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/V films at 900 °C in a quartz tube. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectrum were carried out to characterize the structure, morphology, and photoluminescence properties of GaN sample. The results show that the GaN nanowires and nanorods with pure hexagonal wurtzite structure have good emission properties. The growth direction of nanostructures is perpendicular to the fringes of (1 0 1) plane. The growth mechanism is also briefly discussed.     

Mechanochemical Synthesis and Characterization of GaN Nanocrystals

A solid-state displacement reaction of Ga₂O₃ with Mg₃N₂ has been used to synthesize GaN nanocrystals by mechanochemical processing. X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) measurements indicated that the nanocrystals had a hexagonal structure and sizes ranging from 4 to 20nm. Optical absorption and transmission measurement showed the bandgap of the nanocrystals was consistent with that of bulk GaN samples (3.43eV). This study demonstrates that mechanochemical processing has significant potential for the synthesis of GaN nanocrystals in a simple and efficient way.     

Growth and characterization of high-quality GaN nanowires by ammonification technique

GaN nanowires were successfully synthesized at high quality and large yield on Si (1 1 1) substrate through ammoniating Ga₂O₃/BN films deposited by radio frequency (RF) magnetron sputtering system. X-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR) and selected-area electron diffraction (SAED) confirm that the as-synthesized nanowires are of a hexagonal GaN with wurtzite structure. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) reveal that the nanowires have a straight and smooth curved structure with extremely uniform diameter of about 60 nm, which is helpful to the application of GaN nanowires. The present results demonstrate that the BN is a very important intermedium in the growth of GaN nanowires by this method.     

Synthesis and optical properties of single crystalline GaN nanorods with a rectangular cross-section

GaN nanorods were synthesized from the reaction of a Ga/Ga₂O₃ mixture with NH₃ on Si substrates by chemical vapor deposition. The synthesized products were characterized by scanning and transmission electron microscopy, X-ray diffraction, photoluminescence and Raman spectroscopy. The nanorods are highly single crystalline and possess uniform smooth surfaces. PL revealed only a strong emission at 3.268 eV, ascribed to free exciton (FX) transitions, at room temperature; while the well-known yellow luminescence band centered at 2.2-2.3 eV was not detected. Four first-order phonon modes, corresponding to the A₁(TO), E₁(TO), E₂(high), and A₁(LO) at ∼531, 554, 564, and 721 cm⁻¹, respectively, were observed by Raman backscattering. The red-shift of the FX emission peak and the down-shifts of the Raman modes by a few wave numbers are attributed to the presence of tensile strain inside GaN nanorods.     

Influence of ammoniating temperature on Co-catalyzed GaN nanowires

GaN nanowires (NWS) were synthesized at different temperatures by ammoniating Ga₂O₃/Co films deposited on Si (111) substrate. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), Fourier transformed infrared spectra (FTIR) and photoluminence (PL) spectra were used to characterize the influences of the ammoniating temperature on the morphology, crystallinity and optical properties of GaN NWS. Our results indicate that the samples are all of wurtzite structure and also show that the GaN NWS ammoniated at 950 °C have the best morphology and crystallinity with a single-crystalline structure, and at this temperature the PL spectrum with the strongest ultraviolet (UV) peak is observed. PACS 61.46.-w; 71.55.Eq; 81.15.Cd; 81.07.-b; 61.10.Nz     

Synthesis of large-scale GaN nanowires by ammoniating Ga2O3 films on Co layer deposited on Si（111） substrates

A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed.     

Synthesis and characterization of GaN nanowires

In this work, GaN nanowires were fabricated on Si substrates coated with NiCl₂ thin films using chemical vapor deposition (CVD) method by evaporating Ga₂O₃ powder at 1100 °C in ammonia gas flow. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM) and photoluminescence (PL) spectrum are used to characterize the samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure. The growth mechanism of GaN nanowires is also discussed.     

Structural characterisation of GaAlN/GaN HEMT heterostructures

(GaN/GaAlN/GaN)//Al₂O₃(00.1) HEMT heterostructures have been studied by X-ray scattering techniques, transmission electron microscopy and atomic force microscopy. X-ray reflectometry has been used to determine with a high accuracy both the individual layer thicknesses and the interfacial roughness, in spite of the weak electronic density contrast between layers. From the Fourier inversion method and using a simulation software, the roughness of the interface corresponding to the two-dimensional electron gas location has been determined equal to 0.5 nm. Both high resolution X-ray diffraction and transmission electron microscopy experiments have shown the excellent crystallinity of the heterostructures. Finally, the surface morphology has been inferred using atomic force microscopy experiments.     

Large-scale synthesis and photoluminescence properties of?SiC networks

By using a novel and low-cost microwave method, three-dimensional SiC networks have been synthesized in large-scale. The composition and structural features of the product were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The results show that the SiC networks consist of nanocable X-junction and Y-junction. Some nanocables are composed of 3C–SiC multicore encapsulated in single amorphous SiO₂ shell. The SiC networks emitted stable violet–blue light around 380 nm under 325-nm excitation. Compared to the emission peak of the SiC networks after etched and the reported results of 3C–SiC nanowires, the emission peak of the SiC networks shows significant blueshift. The origin of the photoluminescence for the SiC networks could be due to two possible reasons: the central crystalline SiC nanowires and amorphous SiO₂ shell. A two-step growth mechanism of the SiC networks was proposed based on the experimental characterizations. The successful synthesis of SiC networks is an important step in the development of SiC-based electronic devices and circuits.     

Investigating stacking faults in nonpolar gallium nitride films using X-ray diffraction

Nonpolar (11-20) GaN films with different basal-plane stacking fault (BSF) densities (determined using transmission electron microscopy) were investigated using X-ray diffraction. Diffuse streaking from I₁ and I₂ BSFs was observed in reciprocal space maps of the 10-10 and 20-20 reflections. X-ray calibration curves for BSF density determination can be plotted using the diffusely scattered intensity of open detector 10-10 or 20-20 ω-scans measured at a fixed, large separation from the peak maximum. However, ab initio determination of stacking fault densities is not possible due to additional broadening from other defects. Similarly, ω-scan peak widths are poor indicators of BSF densities.     

Synthesis of flower-shape clustering GaN nanorods by ammoniating Ga2O3 films

Flower-shape clustering GaN nanorods are successfully synthesized on Si（111） substrates through ammoniating Ga2O3/ZnO films at 950℃. The as-grown products are characterized by x-ray diffraction （XRD）, scanning electron microscope （SEM）, field-emission transmission electron microscope （FETEM）, Fourier transform infrared spectrum （FTIR） and fluorescence spectrophotometer. The SEM images demonstrate that the products consist of flower-shape clustering GaN nanorods. The XRD indicates that the reflections of the samples can be indexed to the hexagonal GaN phase and HRTEM shows that the nanorods are of pure hexagonal GaN single crystal. The photoluminescence （PL） spectrum indicates that the GaN nanorods have a good emission property. The growth mechanism is also briefly discussed.