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1.
We present a systematic study of the current-voltage characteristics and electroluminescence of gallium nitride (GaN) nanowire on silicon (Si) substrate heterostructures where both semiconductors are n-type. A novel feature of this device is that by reversing the polarity of the applied voltage the luminescence can be selectively obtained from either the nanowire or the substrate. For one polarity of the applied voltage, ultraviolet (and visible) light is generated in the GaN nanowire, while for the opposite polarity infrared light is emitted from the Si substrate. We propose a model, which explains the key features of the data, based on electron tunnelling from the valence band of one semiconductor into the conduction band of the other semiconductor. For example, for one polarity of the applied voltage, given a sufficient potential energy difference between the two semiconductors, electrons can tunnel from the valence band of GaN into the Si conduction band. This process results in the creation of holes in GaN, which can recombine with conduction band electrons generating GaN band-to-band luminescence. A similar process applies under the opposite polarity for Si light emission. This device structure affords an additional experimental handle to the study of electroluminescence in single nanowires and, furthermore, could be used as a novel approach to two-colour light-emitting devices. 相似文献
2.
Ella C. Linganiso Rafael Rodrigues Sabelo D. Mhlanga Bonex W. Mwakikunga Neil J. Coville Ivo A. Hümmelgen 《Materials Chemistry and Physics》2013
The wide band-gap semiconductor material gallium nitride was synthesized using a one step microwave-assisted solution phase technique. The synthesized GaN nanocrystals showed an intense ultraviolet-blue emission typical of GaN materials. Hydrostatic pressure sensors were fabricated using a GaN/polyvinyl alcohol (PVA) composite film deposited onto an interdigitated electrode and studied by measuring the change in alternating current conductance of the devices at varied applied pressures. Three different GaN concentrations of 29, 50 and 67% were used. A very high sensitivity in the range 100–200 kPa was observed for these devices. The composite devices demonstrated both response and recovery times of less than 16 s. 相似文献
3.
Aluri GS Motayed A Davydov AV Oleshko VP Bertness KA Sanford NA Mulpuri RV 《Nanotechnology》2012,23(17):175501
We demonstrate a new method for tailoring the selectivity of chemical sensors using semiconductor nanowires (NWs) decorated with metal and metal oxide multicomponent nanoclusters (NCs). Here we present the change of selectivity of titanium dioxide (TiO(2)) nanocluster-coated gallium nitride (GaN) nanowire sensor devices on the addition of platinum (Pt) nanoclusters. The hybrid sensor devices were developed by fabricating two-terminal devices using individual GaN NWs followed by the deposition of TiO(2) and/or Pt nanoclusters (NCs) using the sputtering technique. This paper present the sensing characteristics of GaN/(TiO(2)-Pt) nanowire-nanocluster (NWNC) hybrids and GaN/(Pt) NWNC hybrids, and compare their selectivity with that of the previously reported GaN/TiO(2) sensors. The GaN/TiO(2) NWNC hybrids showed remarkable selectivity to benzene and related aromatic compounds, with no measurable response for other analytes. Addition of Pt NCs to GaN/TiO(2) sensors dramatically altered their sensing behavior, making them sensitive only to methanol, ethanol and hydrogen, but not to any other chemicals we tested. The GaN/(TiO(2)-Pt) hybrids were able to detect ethanol and methanol concentrations as low as 100 nmol mol(-1) (ppb) in air in approximately 100 s, and hydrogen concentrations from 1 μmol mol(-1) (ppm) to 1% in nitrogen in less than 60 s. However, GaN/Pt NWNC hybrids showed limited sensitivity only towards hydrogen and not towards any alcohols. All these hybrid sensors worked at room temperature and are photomodulated, i.e. they responded to analytes only in the presence of ultraviolet (UV) light. We propose a qualitative explanation based on the heat of adsorption, ionization energy and solvent polarity to explain the observed selectivity of the different hybrids. These results are significant from the standpoint of applications requiring room-temperature hydrogen sensing and sensitive alcohol monitoring. These results demonstrate the tremendous potential for tailoring the selectivity of the hybrid nanosensors for a multitude of environmental and industrial sensing applications. 相似文献
4.
Scattering-type apertureless near-field microscopy (ANSOM) provides high-resolution dielectric maps of indium gallium nitride (InGaN) semiconductor nanoparticles at visible (633 nm) wavelengths. A specific size-dependent contrast reversal is observed in the ANSOM images of InGaN nanoparticles grown on a layer of gallium nitride (GaN). Model calculations demonstrate that the observed contrast reversal is the result of the competition between the tip-particle versus tip-substrate dipolar coupling. 相似文献
5.
As an important wide-bandgap semiconductor,gallium nitride (GaN) has attracted considerable attention.This paper describes the use of confocal Raman spectroscop... 相似文献
6.
The voltammetry of solid 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (ITF) at an electrode-microparticle-aqueous (electrolyte) interface generates characteristic current-potential profiles associated with solid-solid-phase transformations. During the reactions, electrolyte ions are included into the TCNQ (cations) and TTF (anions) lattice sites as part of the charge neutralization process. Consequently, electrolyte ion concentration is associated with the reversible potential of the TCNQ0/- and TTF0/+ reactions, making these processes candidates for the development of novel voltammetric cation and anion sensors, respectively. Electrode potential-analyte ion concentration dependence studies exhibited highly reproducible potential shifts of 45 (+/- 1) mV/decade change in ion analyte concentration for both the TCNQ cation sensor and the TTF anion sensor. When presented with mixed-analyte solutions, both ion-sensing systems exhibited a degree of ion selectivity. Ion selectivity trends may be modeled using equations based on a Nicolsky-type selectivity relationship, in accordance with the concept that these are the voltammetric analogies of potentiometric ion-selective membrane electrodes. 相似文献
7.
Zeta potentials of colloidal particles were used to study the influence of anions on the formation of ferric oxide hydroxides [Fe(O)OH]. This anion effect, complexation with ferric ions and adsorption on the resulting particle surface, correlated well with the determined zeta potentials. The greater anion effect in ferric ion solution decreased the measured zeta potential of colloidal particles. This effect increased with increasing size, charge and complexation of anions. The results indicated that the composition and morphology of Fe(O)OH precipitates were affected by the presence of anions in solution. 相似文献
8.
Semiconductor light‐emitting diodes (LEDs), especially GaN‐based heterostructures, are widely used in light illumination. The lack of inversion symmetry of wurtzite crystal structures and the lattice mismatch at heterointerfaces cause large polarization fields with contributions from both spontaneous polarization and piezoelectric polarization, which in turn results in obvious quantum confined stark effect. It is possible to alleviate this effect if the local electrostatic fields and band alignment induced charge redistribution can be quantitatively determined across the heterostructures. In this Concept, the applications of electron holography to investigate semiconductor LEDs are summarized. Following the off‐axis electron holography scheme, the GaN‐based LED heterostructures including InGaN/GaN‐based quantum wells, other GaN‐based quantum wells, and other forms of GaN‐based LED materials are discussed, focusing on the local potential drops, polarization fields, and charge distributions. Moreover, GaAs‐based LED heterostructures are briefly discussed. The in‐line electron holography scheme emphasizes the capability of large area strain mapping across LED heterostructures with high spatial resolution and accuracy, which is combined with quantitative electrostatic measurements and other advanced transmission electron microscopy characterizations to provide an overall nanometer scale perspective of LED devices for further improvement in their electric and optical properties. 相似文献
9.
Persistent Photoconductivity,Nanoscale Topography,and Chemical Functionalization Can Collectively Influence the Behavior of PC12 Cells on Wide Bandgap Semiconductor Surfaces
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Patrick J. Snyder Ronny Kirste Ramon Collazo Albena Ivanisevic 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(24)
Wide bandgap semiconductors such as gallium nitride (GaN) exhibit persistent photoconductivity properties. The incorporation of this asset into the fabrication of a unique biointerface is presented. Templates with lithographically defined regions with controlled roughness are generated during the semiconductor growth process. Template surface functional groups are varied using a benchtop surface functionalization procedure. The conductivity of the template is altered by exposure to UV light and the behavior of PC12 cells is mapped under different substrate conductivity. The pattern size and roughness are combined with surface chemistry to change the adhesion of PC12 cells when the GaN is made more conductive after UV light exposure. Furthermore, during neurite outgrowth, surface chemistry and initial conductivity difference are used to facilitate the extension to smoother areas on the GaN surface. These results can be utilized for unique bioelectronics interfaces to probe and control cellular behavior. 相似文献
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利用热壁化学气相沉积在Si(111)衬底上获得GaN品绳,采用傅里叶红外吸收谱(FTIR)、扫描电子显微镜(SEM)、选区电子衍射(SAED)、X射线衍射(XRD)和光致发光谱(PL)对晶绳进行组成、结构、形貌和光学特性分析。初步结果证明:在Si(111)衬底上获得择优生长的六方纤锌矿结构的GaN晶绳。SEM显示在均匀的薄膜上出现φ6μm的晶绳,FTIR显示GaN薄膜的主要成分为GaN同时含有少量的C污染,由XRD和SAED的综合分析得出晶绳呈六方纤锌矿单晶结构,PL测试表明晶绳呈现不同于GaN薄膜的发光特性。 相似文献
12.
Fuwen Qin Miaomiao Zhong Chong Wang Yuemei Liu Jiming Bian Enping Wang Hui Wang Dong Zhang 《Journal of Materials Science: Materials in Electronics》2013,24(12):5069-5074
Gallium nitride (GaN) films were deposited on Ni metal substrate using electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition system. With this approach, highly c-oriented GaN films with smooth surface were obtained at an extremely low temperature of ~480 °C. The trimethyl gallium (TMGa) flux dependent structural, morphological, and optical characteristics of GaN films were investigated by X-ray diffraction analysis, reflection high energy electron diffraction, atomic force microscopy and photoluminescence analysis. The results indicate that it is feasible to deposit GaN films on Ni metal substrate under the proper deposition procedures. The high quality GaN films with high c-axis orientation and strong ultraviolet emission peak are successfully achieved under the optimized TMGa flux of 1.2 sccm. The GaN/Ni structure has great potential for the development of high power devices with excellent heat dissipation. 相似文献
13.
首先用聚乙烯吡咯烷酮(PVP)作为表面活性剂, 硝酸镓[Ga(NO3)3]作为镓源, 采用溶胶-凝胶法制备了GaN粉末。然后通过固相法将GaN粉末和ZnO粉末按不同配比机械混合, 制备成GaN/ZnO复合体。采用X射线粉末衍射(XRD)、扫描电镜(SEM)、X射线能谱 (EDS)、高分辨透射电子显微镜(HRTEM)和发致光谱(PL)表征GaN/ZnO复合体的微结构、形貌、成分和发光特性, 并将其作为催化剂进行降解亚甲基蓝水溶液的光催化性能测试。结果表明: GaN/ZnO复合体对比未经复合的GaN和ZnO粉末, 光催化性能有明显的增强。基于一级动力学方程分析, 当GaN/ZnO复合体中GaN粉末和ZnO粉末含量配比为1: 2时, 光催化性能达到最佳, 其速率常数k值为0.11 min-1。 相似文献
14.
Fu-Wen Qin Miao-Miao Zhong Yue-Mei Liu Hui Wang Ji-Ming Bian Chong Wang Yue Zhao Dong Zhang Qin-ming Li 《Journal of Materials Science: Materials in Electronics》2014,25(2):969-973
A low temperature growth method based on electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition system (ECR-PEMOCVD) was proposed for the growth of gallium nitride (GaN) films on ordinary soda-lime glass substrates with sputtered Cu as intermediate layer (Cu/glass substrates). The influence of deposition temperature on the properties of the GaN films on Cu/glass substrates was systematically investigated by means of In-situ reflection high energy electron diffraction, X-ray diffraction, atomic force microscopy and photoluminescence spectra. With this method, high c-orientated crystalline GaN films with relatively smooth surface were achieved on amorphous Cu/glass substrate at an extremely low temperature of ~400 °C. The successfully growth of crystalline GaN films on amorphous Cu/glass substrates show great potential for significant improvements in the scalability and cost of GaN based devices, since the adverse effects with high temperature process for glass substrates can be effectively suppressed by this technique. 相似文献
15.
The morphology, structure, and optical properties of gallium nitride (GaN) nanowires grown using metal-organic chemical vapor deposition (MOCVD) on r-plane sapphire using gold and nickel seed particles were investigated. We found that different seed particles result in different growth rates and densities of structural defects in MOCVD-grown GaN nanowires. Ni-seeded GaN nanowires grow faster than Au-seeded ones, and they do not contain the basal plane stacking faults that are observed in Au-seeded GaN nanowires. We propose that stacking fault formation is related to the supersaturation and surface energies in different types of seed particles. Room temperature photoluminescence studies revealed a blue-shifted peak in Au-seeded GaN nanowires compared to the GaN near-bandgap emission. The blue-shifted peak evolves as a function of the growth time and originates from the nanowire base, likely due to strain and Al diffusion from the substrate. Our results demonstrate that seed particle composition has a direct impact on the growth, structure, and optical properties of GaN nanowires and reveal some general requirements for seed particle selection for the growth of compound semiconductor nanowires. 相似文献
16.
The mechanism of ultraviolet laser ablation of GaN epitaxial films is determined: it is found to be based on the dissociation
of GaN molecules to form volatile nitrogen-containing components. The conditions of exposure under which the formation of
gallium nanoclusters on the GaN surface are determined. Regimes of epitaxial growth of GaN are found in which parallel microterraces
form on the surface of the samples. It is found that when samples with microterraces in the as-grown state are irradiated
by high-power ultraviolet radiation, gallium nanowires are formed on the surface. It is proposed to use these phenomena to
develop new UV optical lithographic techniques and to fabricate single-electron devices based on GaN.
Pis’ma Zh. Tekh. Fiz. 25, 13–18 (May 26, 1999) 相似文献
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The retention mechanism of electrostatic ion chromatography (EIC) is currently under debate and is the focus of this paper. A comprehensive set of retention data has been obtained on a C18 column coated with the zwitterionic surfactant 3-(N,N-dimethylmyristylammonio)propanesulfonate used with a range of mobile phases in which both the mobile-phase anion and cation have been varied systematically. Electro-osmotic flow measurements were also obtained on fused-silica capillaries coated with the zwitterion (and also some monofunctional surfactants) and were used to evaluate the nature of the surface charge on the layer of adsorbed surfactant in the presence of various background electrolytes. A new retention mechanism for EIC was developed on the basis of these data. This mechanism proposes that equilibration of the bound zwitterions with a mobile phase containing a suitable electrolyte causes the establishment of a charged layer created by the terminal sulfonate groups of the zwitterion, which acts as a Donnan membrane. The magnitude and polarity of the charge on this membrane depends on the nature of the mobile-phase ions. The Donnan membrane exerts weak electrostatic repulsion or attraction effects on analyte anions. A second component of the retention mechanism is chaotropic interaction of the analyte anion with the quaternary ammonium functional group of the zwitterion. This interaction exerts the major effect on the separation selectivity of EIC, such that analyte anions are eluted in order of increasing chaotropic interactions in accordance with the Hofmeister series. 相似文献
19.
Recent Progress on Piezotronic and Piezo‐Phototronic Effects in III‐Group Nitride Devices and Applications
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20.
《Materials science & engineering. C, Materials for biological applications》2006,26(2-3):462-471
Ion exchange phenomena have been investigated in a polymeric anion-exchange membrane prepared from cross-linked silicone polymer grafted with cationic groups. The affinity of different anions towards the membrane was inferred from impedance measurements in a electrolyte/insulator/semiconductor (EIS) electrochemical set up, allowing the survey of the detection limit, flat band potential and capacity variations. The selectivity of ion-exchange for a series of anions having a the same electrical charge followed the Hofmeister series. It was found that the affinity of anions and the electrical potential variations were related because the anion exchange inside the bulk of the membrane was correlated with the adsorption of anions at its surface. Electrical capacity measurements gave supplementary information which was difficult to rationalize because they depended on several parameters. 相似文献