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.     

Synthesis of GaN nanochestnuts by hydride vapour phase epitaxy

GaN nanochestnuts with numerous nanorods and nanoneedles were synthesized on AlN/Si(111) substrate using hydride vapour phase epitaxy (HVPE) method under constant N₂ carrier gas flow rate. The formation process of nanochestnuts was systematically investigated and discussed on the basis of the experimental results. The nanochestnuts were analyzed by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and cathodoluminescence (CL). GaN nanochestnuts were revealed as the composition of core, circular stacking layers, and surrounded with nanorods or nanoneedles on all sides. The resultant nanochestnuts may be a promising structure for omnidirectional nano device applications in the future.     

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.     

InGaN/GaN multiple quantum wells grown on nonpolar facets of vertical GaN nanorod arrays

Uniform GaN nanorod arrays are grown vertically by selective area growth on (left angle bracket 0001 right angle bracket) substrates. The GaN nanorods present six nonpolar {1?100} facets, which serve as growth surfaces for InGaN-based light-emitting diode quantum well active regions. Compared to growth on the polar {0001} plane, the piezoelectric fields in the multiple quantum wells (MQWs) can be eliminated when they are grown on nonpolar planes. The capability of growing ordered GaN nanorod arrays with different rod densities is demonstrated. Light emission from InGaN/GaN MQWs grown on the nonpolar facets is investigated by photoluminescence. Local emission from MQWs grown on different regions of GaN nanorods is studied by cathodoluminescence (CL). The core-shell structure of MQWs grown on GaN nanorods is investigated by cross-sectional transmission electron microscopy in both axial and radial directions. The results show that the active MQWs are predominantly grown on nonpolar planes of GaN nanorods, consistent with the observations from CL. The results suggest that GaN nanorod arrays are suitable growth templates for efficient light-emitting diodes.     

Catalyst-free GaN nanorods grown by metalorganic molecular beam epitaxy

High-density GaN nanorods with outstanding crystal quality were grown on c-sapphire substrates by radio-frequency plasma-assisted metalorganic molecular beam epitaxy under catalyst- and template-free growth condition. Morphological and structural characterization of the GaN nanorods was employed by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy (HRTEM). These results indicate that the rod number density can reach 1/spl times/10/sup 10/ cm/sup -2/ and the nanorods are well-aligned with preferentially oriented in the c-axis direction. Meanwhile, no metallic (Ga) droplet was observed at the end of the rods, which is the intrinsic feature of vapor-liquid-solid method. Nanorods with no traces of any extended defects, as confirmed by TEM, were obtained as well. In addition, optical investigation was carried out by temperature- and power-dependent micro-photoluminescence (/spl mu/-PL). The PL peak energies are red-shifted with increasing excitation power, which is attributed to many-body effects of free carriers under high excitation intensity. The growth mechanism is discussed on the basis of the experimental results. Catalyst-free GaN nanorods presented here might have a high potential for applications in nanoscale photonic devices.     

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.     

High quality GaN film overgrown on GaN nanorods array template by HVPE

The high density vertically aligned GaN nanorods array was fabricated by thermal evaporation of GaN powder with the assistance of HCl gas. The GaN nanorods array was used as template for GaN film growth by hydride vapor phase epitaxy (HVPE). The full width at half maximum values (FWHM) of high-resolution X-ray diffraction (HRXRD) rocking curves for the GaN film with GaN nanorods array template are 247 arc sec (002 reflection) and 308 arc sec (102 reflection), while those for the GaN film without GaN nanorods array template are 292 and 369 arc sec, respectively. This result indicates a significant reduction of dislocation density in the overgrown GaN film with GaN nanorods array template. Photoluminescence spectra measurements reveal the compressive strain relaxation and an improvement in the quality of the overgrown GaN film with GaN nanorods array template as compared to the regrown GaN film without GaN nanorods array template, which is consistent with the trend observed by HRXRD.     

微波水热及氨化法制备GaN纳米棒

以Ga2O3为原料,用微波水热法和高温氨化两步法合成GaN纳米棒。采用XRD及SEM对其结晶形貌进行表征。研究得出,GaN纳米粉呈长径比约为5:1的棒状,该纳米棒是由沿(002)方向高度取向一致的GaN晶粒结晶而成。XRD分析显示,GaN纳米棒为六方纤锌矿结构且结晶良好。光致发光(PL)分析显示,合成纳米棒在367nm处存在GaN本征发光峰。中心位于468nm、493nm及534nm附近出现了宽而弱的发射带,这有助于GaN在光电领域的应用。     

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.     

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.     

化学气相沉积法制备GaN纳米线和纳米棒

采用浸渍法在未抛光的硅衬底上涂抹一层NiCl2薄膜,通过化学气相沉积法(CVD)制备出高质量的GaN纳米线和纳米棒.X射线衍射(XRD)、傅立叶红外吸收光谱(FTIR)、选区电子衍射(SAED)和高分辨透射电子显微镜(HRTEM)的分析结果表明,采用此方法得到了六方纤锌矿结构的GaN单晶纳米线.通过扫描电镜(SEM)观察发现纳米线的形貌,纳米线的直径在50～200nm之间,纳米棒的直径在200～800nm之间.     

Structure and optical spectrum of GaN nanorods produced on Si(111) substrates

A novel method is applied to prepare nanorods. In this method, nanorods have been successfully synthesized on Si(111) substrates through annealing sputtered Ga₂O₃/Nb films under flowing ammonia at 950 °C in a quartz tube. The as-synthesized nanorods are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The results show that the nanorod is single-crystalline GaN. It has a diameter of about 200 nm and lengths typically up to several micrometers. Photoluminescence spectrum under excitation at 325 nm only exhibits a UV light emission peak is located at about 368.5 nm. Finally, the growth mechanism of nanorods is also briefly discussed.     

Optical Properties of Mn-Implanted GaN Nanorods

We have investigated the optical properties of vertical GaN nanorods with diameters of 150 nm grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy followed by Mn ion implantation and annealing. The GaN nanorods are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photoluminescence excitonic lines near 3.47 eV. For GaMnN nanorods, Arrhenius plots of the intensities of the Mn acceptor give a thermal activation energy of Δ=350 meV, indicating that the thermal quenching of the Mn-related PL peak is due to the dissociation of an acceptor-bound hole from the temperature-dependent PL spectra. This suggests that the Mn-bound holes in GaN nanorods exhibit the impurity states predicted by the hydrogen model.     

Optical properties of GaN nanorods grown by molecular-beam epitaxy; dependence on growth time

The growth and optical properties of GaN nanorods grown on Si(111) substrates by rf plasma assisted molecular-beam epitaxy are investigated by means of field emission scanning electron microscopy and photoluminescence measurements as a function of growth time. It is clearly demonstrated that the rate of growth of the nanorod diameter starts to increase after ～90?min because of the coalescence of neighbouring nanorods. And the optical properties of the samples grown at a high growth rate are dramatically changed due to induced defects. The critical diameter for defect-free GaN nanorods is determined as below ～140?nm under N-rich conditions.     

The novel bicrystalline GaN nanorods

High-quality bicrystalline GaN nanorods (BGNs) are fabricated by a reasonable approach, where physical vapour deposition is involved in 1300 °C. X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM observations show that the as-synthesized BGNs have an interesting bicrystal phase, and a uniform diameter of about 50 nm and length up to a few microns. We demonstrate that BGNs are controlled by conventional vapor–liquid–solid (VLS) mechanism.     

One-pot simple synthesis and characterisation of Mn2+-doped GaN nanorods by RAPET method

In this work, we display one-step reactions under autogenic pressure at elevated temperature (RAPET) method-based synthesis of Mn-doped GaN nanorods by varying the atomic ratio of Mn:Ga as 0, 0.02, 0.04, 0.06 and 0.08, respectively. The synthesised nanorods are characterised by X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and Raman spectral methods. It is observed that there is a decrease in the lattice constant with an increase in the concentration of Mn (from 0.02 to 0.08 wt%). Moreover, the smaller covalent radius of Mn is the key for the doping process. The Mn-doped GaN nanocrystals show rod-like morphology with a length of 40–50 nm and width of 8–12 nm. This size factor mainly depends on the doping of Mn [from transmission electron microscopy (TEM) analysis] into GaN components. Well-defined lattice fringes are elucidated for the growth of crystalline hexagonal GaN (wurtzite type) nanocrystals.     

Fabrication of GaN nanorods by inductively coupled plasma etching via SiO2 nanosphere lithography

In this study, we present a facile route to fabricate GaN nanorods by employing the nanosphere lithography (NSL) technique. Compared to previous approaches, it was demonstrated that arrays of silica (SiO₂) nanospheres can be effectively used as etching masks for the inductively coupled plasma etching process. By adjusting the etching conditions between SiO₂ nanospheres and GaN substrates, well-defined nanorods, which were as long as a few microns with controllable diameters, were successfully fabricated. This method is much simpler than any other technique currently being used, and can be generally applied to fabricate various types of nanorods.     

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.     

Self-assembled GaN nanowires on diamond

We demonstrate the nucleation of self-assembled, epitaxial GaN nanowires (NWs) on (111) single-crystalline diamond without using a catalyst or buffer layer. The NWs show an excellent crystalline quality of the wurtzite crystal structure with m-plane faceting, a low defect density, and axial growth along the c-axis with N-face polarity, as shown by aberration corrected annular bright-field scanning transmission electron microscopy. X-ray diffraction confirms single domain growth with an in-plane epitaxial relationship of (10 ?10)(GaN) [parallel] (01 ?1)(Diamond) as well as some biaxial tensile strain induced by thermal expansion mismatch. In photoluminescence, a strong and sharp excitonic emission reveals excellent optical properties superior to state-of-the-art GaN NWs on silicon substrates. In combination with the high-quality diamond/NW interface, confirmed by high-resolution transmission electron microscopy measurements, these results underline the potential of p-type diamond/n-type nitride heterojunctions for efficient UV optoelectronic devices.     

Acoustic charge transport in GaN nanowires

We present acoustic charge transport in GaN nanowires (GaN NWs). The GaN NWs were grown by molecular beam epitaxy (MBE) on silicon(111) substrates. The nanowires were removed from the silicon substrate, aligned using surface acoustic waves (SAWs) on the piezoelectric substrate LiNbO(3) and finally contacted by electron beam lithography. Then, a SAW was used to create an acoustoelectric current in the GaN NWs which was detected as a function of radio-frequency (RF) wave frequency and its power. The presented method and our experimental findings open up a route towards new acoustic charge transport nanostructure devices in a wide bandgap material such as GaN.