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Showing papers on "Doping published in 2006"


Patent
22 Nov 2006
TL;DR: In this article, a transparent conductive film is produced by growing ZnO doped with a group III element oxide on a substrate and has a region with a crystal structure in which a c-axis grows along a plurality of different directions.
Abstract: A ZnO-based transparent conductive film is produced by growing ZnO doped with a group III element oxide on a substrate and has a region with a crystal structure in which a c-axis grows along a plurality of different directions. The transparent conductive film produced by growing ZnO doped with a group III element oxide on a substrate has a ZnO (002) rocking curve full width at half maximum of about 13.5° or more. ZnO is doped with a group III element oxide so that the ratio of the group III element oxide in the transparent conductive film is about 7% to about 40% by weight. The transparent conductive film is formed on the substrate with a SiNx thin film provided therebetween. The transparent conductive film is formed on the substrate by a thin film formation method with a bias voltage applied to the substrate.

1,021 citations


Journal ArticleDOI
TL;DR: Nitrogen doping-induced changes in the electronic properties, defect formation, and surface structure of TiO2 rutile(110) and anatase(101) single crystals were investigated and thermal instability may degrade the catalyst during applications.
Abstract: Nitrogen doping-induced changes in the electronic properties, defect formation, and surface structure of TiO2 rutile(110) and anatase(101) single crystals were investigated. No band gap narrowing is observed, but N doping induces localized N 2p states within the band gap just above the valence band. N is present in a N(III) valence state, which facilitates the formation of oxygen vacancies and Ti 3d band gap states at elevated temperatures. The increased O vacancy formation triggers the 1 x 2 reconstruction of the rutile (110) surface. This thermal instability may degrade the catalyst during applications.

639 citations


Journal ArticleDOI
TL;DR: In this paper, the magnetic properties of carbon-doped ZnO were investigated and it was shown that carbon substitution for oxygen results in a magnetic moment of 1.78 -3.0 \mu_B$ per carbon.
Abstract: We report magnetism in carbon doped ZnO. Our first-principles calculations based on density functional theory predicted that carbon substitution for oxygen in ZnO results in a magnetic moment of 1.78 $\mu_B$ per carbon. The theoretical prediction was confirmed experimentally. C-doped ZnO films deposited by pulsed laser deposition with various carbon concentrations showed ferromagnetism with Curie temperatures higher than 400 K, and the measured magnetic moment based on the content of carbide in the films ($1.5 - 3.0 \mu_B$ per carbon) is in agreement with the theoretical prediction. The magnetism is due to bonding coupling between Zn ions and doped C atoms. Results of magneto-resistance and abnormal Hall effect show that the doped films are $n$-type semiconductors with intrinsic ferromagnetism. The carbon doped ZnO could be a promising room temperature dilute magnetic semiconductor (DMS) and our work demonstrates possiblity of produing DMS with non-metal doping.

622 citations


Journal ArticleDOI
TL;DR: In this paper, self-organized anodic titania nanotube layers were doped with nitrogen successfully using ion implantation, resulting in a N-doped crystalline anatase nanotubite structure with strongly enhanced photocurrent response in both the UV and the visible range.
Abstract: Self-organized anodic titania nanotube layers were doped with nitrogen successfully using ion implantation. Photoelectrochemical measurements combined with XRD measurements show that the damage created by ion bombardment (that leads to a drastic decrease of the photoconversion efficiency) can be “annealed out” by an adequate heat treatment. This results in a N-doped crystalline anatase nanotube structure with strongly enhanced photocurrent response in both the UV and the visible range.

522 citations


Patent
04 Oct 2006
TL;DR: A bulk-doped semiconductor is a semiconductor that is at least one of the following: a single crystal, an elongated and bulk-depletioned semiconductor with a largest cross-sectional dimension less than 500 nanometers as discussed by the authors.
Abstract: A bulk-doped semiconductor that is at least one of the following: a single crystal, an elongated and bulk-doped semiconductor that, at any point along its longitudinal axis, has a largest cross-sectional dimension less than 500 nanometers, and a free-standing and bulk-doped semiconductor with at least one portion having a smallest width of less than 500 nanometers. Such a semiconductor may comprise an interior core comprising a first semiconductor; and an exterior shell comprising a different material than the first semiconductor. Such a semiconductor may be elongated and may have, at any point along a longitudinal section of such a semiconductor, a ratio of the length of the section to a longest width is greater than 4:1, or greater than 10:1, or greater than 100:1, or even greater than 1000:1. At least one portion of such a semiconductor may a smallest width of less than 200 nanometers, or less than 150 nanometers, or less than 100 nanometers, or less than 80 nanometers, or less than 70 nanometers, or less than 60 nanometers, or less than 40 nanometers, or less than 20 nanometers, or less than 10 nanometers, or even less than 5 nanometers. Such a semiconductor may be a single crystal and may be free-standing. Such a semiconductor may be either lightly n-doped, heavily n-doped, lightly p-doped or heavily p-doped. Such a semiconductor may be doped during growth. Such a semiconductor may be part of a device, which may include any of a variety of devices and combinations thereof, and a variety of assembling techniques may be used to fabricate devices from such a semiconductor. Two or more of such a semiconductors, including an array of such semiconductors, may be combined to form devices, for example, to form a crossed p-n junction of a device. Such devices at certain sizes may exhibit quantum confinement and other quantum phenomena, and the wavelength of light emitted from one or more of such semiconductors may be controlled by selecting a width of such semiconductors. Such semiconductors and device made therefrom may be used for a variety of applications.

460 citations


Journal ArticleDOI
TL;DR: In this paper, the photocatalytic activity of Cr-TiO2 was investigated for the degradation of XRG aqueous solution both under UV and visible light irradiation with an optimal doping concentration of 0.15% and 0.2%, respectively.
Abstract: Cr3+-doped anatase titanium dioxide photocatalysts were prepared by the combination of sol–gel process with hydrothermal treatment. The samples were characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area (SBET), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was confirmed that Cr substitutes Ti4+ in TiO2 lattice in trivalent ionic state, and the concentrations of dopants Cr3+ decrease from the exterior to the interior of doped TiO2. The photocatalytic activity of Cr-TiO2 was investigated for the photocatalytic degradation of XRG aqueous solution both under UV and visible light irradiation. Due to the excitation of 3d electron of Cr3+ to the conduction band of TiO2, Cr-TiO2 shows a good ability for absorbing the visible light to degrade XRG. Doping of chromium ions effectively improves the photocatalytic activity under both UV light irradiation and visible light irradiation with an optimal doping concentration of 0.15% and 0.2%, respectively. The special distribution of dopants Cr3+ seems having a good effect on enhancing the photocatalytic activity of Cr-TiO2.

428 citations


Journal ArticleDOI
TL;DR: A family of soluble narrow band gap donor-acceptor conjugated polymers based on dioxythiophenes and cyanovinylenes is reported, which show three accessible color states changing from an absorptive blue or purple in the neutral state to a transmissive sky-blue or gray in the oxidized and reduced forms.
Abstract: A family of soluble narrow band gap donor-acceptor conjugated polymers based on dioxythiophenes and cyanovinylenes is reported. The polymers were synthesized using Knoevenagel polycondensation or Yamamoto coupling polymerizations to yield polymers with molecular weights on the order of 10 000-20 000 g/mol, which possess solubility in common organic solvents. Thin film optical measurements revealed narrow band gaps of 1.5-1.8 eV, which gives the polymers a strong overlap of the solar spectrum. The energetic positions of the band edges were determined by cyclic voltammetry and differential pulse voltammetry and demonstrate that the polymers are both air stable and show a strong propensity for photoinduced charge transfer to fullerene acceptors. Such measurements also suggest that the polymers can be both p- and n-type doped, which is supported by spectroelectrochemical results. These polymers have been investigated as electron donors in photovoltaic devices in combination with PCBM ([6,6]-phenyl C(61)-butyric acid methyl ester) as an electron acceptor based on the near ideal band structures designed into the polymers. Efficiencies as high as 0.2% (AM1.5) with short circuit current densities as high as 1.2-1.3 mA/cm(2) have been observed in polymer/PCBM (1:4 by weight) devices and external quantum efficiencies of more than 10% have been observed at wavelengths longer than 600 nm. The electrochromic properties of the narrow band gap polymers are also of interest as the polymers show three accessible color states changing from an absorptive blue or purple in the neutral state to a transmissive sky-blue or gray in the oxidized and reduced forms. The wide electrochemical range of electrochromic activity coupled with the strong observed changes in transmissivity between oxidation states makes these materials potentially interesting for application to electrochromic displays.

387 citations


Journal ArticleDOI
TL;DR: Being optically transparent with the above optimal properties, Cr-doped In2O3 emerges as a viable candidate for the development of spin electronics.
Abstract: The search for an ideal magnetic semiconductor with tunable ferromagnetic behaviour over a wide range of doping or by electrical gating is being actively pursued as a major step towards realizing spin electronics. A magnetic semiconductor having a high Curie temperature, capable of independently controlled carrier density and magnetic doping, is crucial for developing spin-based multifunctional devices. Cr-doped In2O3 is such a unique system, where the electrical and magnetic behaviour—from ferromagnetic metal-like to ferromagnetic semiconducting to paramagnetic insulator—can be controllably tuned by the defect concentration. An explicit dependence of magnetic interaction leading to ferromagnetism on the carrier density is shown. A carrier-density-dependent high Curie temperature of 850–930 K has been measured, in addition to the observation of clear magnetic domain structures in these films. Being optically transparent with the above optimal properties, Cr-doped In2O3 emerges as a viable candidate for the development of spin electronics.

372 citations


Journal ArticleDOI
TL;DR: In this article, high-quality transparent conductive gallium-doped ZnO (GZO) thin films were deposited on quartz glass substrates using pulsed laser deposition.

371 citations


Journal ArticleDOI
TL;DR: In this article, the effects of annealing temperature and dopant concentration on the structural and optical properties of ZnO:Al, AZO thin films have been discussed and the minimum sheet resistance of 10 4 ǫ/□ was obtained for the film doped with 1.6% Al, annealed at 750°C.

357 citations


Journal ArticleDOI
TL;DR: ZnO nanocrystals doped with Cd, Mg, Mn, and Fe ions were obtained by thermolysis of a family of metal cupferrates and are sufficiently defect-free to exhibit band edge luminescence.
Abstract: ZnO nanocrystals doped with Cd, Mg, Mn, and Fe ions were obtained by thermolysis of a family of metal cupferrates. The nanocrystals were characterized by X-ray diffraction, energy-dispersive X-ray analysis, transmission electron microscopy, UV-visible, luminescence, and excitation spectroscopy. The band gap of the nanocrystals can be tuned in the range of 2.9-3.8 eV by the use of the dopants. In most cases, the nanocrystals are sufficiently defect-free to exhibit band edge luminescence.

Journal ArticleDOI
TL;DR: In this article, the first-principles calculations of doping effects in ZnO with group-IB elements such as Cu, Ag, and Au were presented, and the calculated transition energies were 0.7, 0.4, and 0.5eV, respectively.
Abstract: The authors present their first-principles calculations of doping effects in ZnO with group-IB elements such as Cu, Ag, and Au. The calculated transition energies e(0∕−) for substitutional Cu, Ag, and Au are 0.7, 0.4, and 0.5eV, respectively. The calculated formation energies are very low for these group-IB elements on the substitutional sites, but rather high at the interstitial sites under oxygen-rich growth conditions. Under the conditions, the formation of major hole-killer defects, such as oxygen vacancies and Zn interstitial, are suppressed. Thus, Ag may be a good candidate for producing p-type ZnO.

Journal ArticleDOI
TL;DR: The etching process features weak dependence on the doping of the silicon wafers and, thus, provides an efficient method to prepare silicon nanowires with desirable doping characteristics.
Abstract: A straightforward metal-particle-induced, highly localized site-specific corrosion-like mechanism was proposed for the formation of aligned silicon-nanowire arrays on silicon in aqueous HF/AgNO3 solution on the basis of convincing experimental results. The etching process features weak dependence on the doping of the silicon wafers and, thus, provides an efficient method to prepare silicon nanowires with desirable doping characteristics. The novel electrochemical properties between silicon and active noble metals should be useful for preparing novel silicon nanostructures and also new optoelectronic devices.

Journal ArticleDOI
TL;DR: In this paper, the metal-semiconductor transition behavior observed in transparent and conducting ZnO:Ga films grown by pulsed-laser deposition was investigated, and the electrical resistivity measurements were carried out on ZnOs with varying Ga concentration in the temperature range of 14to300K.
Abstract: In this paper, we report on the metal-semiconductor transition behavior observed in transparent and conducting ZnO:Ga films grown by pulsed-laser deposition. The electrical resistivity measurements were carried out on ZnO films with varying Ga concentration in the temperature range of 14to300K. The electrical properties were correlated with film structure, and detailed structural characterization was performed using x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. The room-temperature resistivity of these films was found to decrease with Ga concentration up to 5% Ga, and then increase. The lowest value of resistivity (1.4×10−4Ωcm) was found at 5% Ga. Temperature dependent resistivity measurements showed a metal-semiconductor transition, which is rationalized by localization of degenerate electrons. A linear variation of conductivity with T below the transition temperature suggests that the degenerate electrons are in a weak-localization regime. It was also found t...

Journal ArticleDOI
TL;DR: In this paper, a theoretical investigation of anion doping in TiO2 and its effects on the electronic structure and subsequently the photoactivity is presented. And the effects of doping concentration on the localization properties of the valence band edge are discussed.
Abstract: Previous experimental studies describe an efficient photoresponse in the visiblelight region for anion-doped TiO2 .D oping with carbon, nitrogen, as well as sulfur, yields promising second-generation photocatalysis with TiO2 .W e present a theoretical investigatio no fs ubstitutional anion doping in TiO2 and discuss doping effects on the electronic structure, and subsequently the photoactivity. The resulting bandgap narrowing predicted in this work is consistent with experimental observations. Furthermore, we discuss the effects of doping concentration on the localization properties of the valence band edge. Ou rs ystematic study of anion-doped TiO2 implies that the carbon-doped TiO2 is the most promising due to a significant overlap between the O 2p state and the carbon states near the valence band edge. Additionally, carbon dopants produce th el argest valence band red shift of the three anion-doped TiO2 studied.

PatentDOI
TL;DR: A micrometer-scale ion trap, fabricated on a monolithic chip using semiconductor microelectromechanical systems (MEMS) technology, is described in this paper, where a single 111Cd+ ion is confined, laser cooled, and the heating measured in an integrated radiofrequency trap etched from a doped gallium arsenide (GaAs) heterostructure.
Abstract: A micrometer-scale ion trap, fabricated on a monolithic chip using semiconductor micro-electromechanical systems (MEMS) technology. A single 111Cd+ ion is confined, laser cooled, and the heating measured in an integrated radiofrequency trap etched from a doped gallium arsenide (GaAs) heterostructure. Single 111Cd+ qubit ions are confined in a radiofrequency linear ion trap on a semiconductor chip by applying a combination of static and oscillating electric potentials to integrated electrodes. The electrodes are lithographically patterned from a monolithic semiconductor substrate, eliminating the need for manual assembly and alignment of individual electrodes. The scaling of this structure to hundreds or thousands of electrodes is possible with existing semiconductor fabrication technology.

Journal ArticleDOI
TL;DR: In this article, the structural properties of undoped and manganese doped zinc oxide (ZnO) thin films were studied using X-ray diffraction, and it was found that the undoped ZnO films exhibit hexagonal wurtzite structure with strong c-axis orientation.

Journal ArticleDOI
TL;DR: In this article, the metallic conductivity in Ga:ZnO system at room temperature and a metal-semiconductor transition (MST) behavior at low temperatures was reported.
Abstract: This letter reports the metallic conductivity in Ga:ZnO system at room temperature and a metal-semiconductor transition (MST) behavior at low temperatures. Zn0.95Ga0.05O films, deposited by pulsed laser deposition in the pressure range of ∼10−2Torr of oxygen, were found to be crystalline and exhibited degeneracy at room temperature with the electrical resistivity close to 1.4×10−4Ωcm and transmittance >80% in the visible region. Temperature dependent resistivity measurements of these highly conducting and transparent films also showed, for the first time, a MST at ∼170K. Mechanisms responsible for these observations are discussed in the terms of dopant addition and its effect on ionization efficiency of oxygen vacancies.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the electron control and electron transport mechanisms on amorphous indium zinc oxide (IZO) films and confirmed that H2 introduction into the IZO deposition process was effective to increase carrier density.

Journal ArticleDOI
23 Nov 2006-Nature
TL;DR: It is reported that superconductivity can be induced when boron is locally introduced into silicon at concentrations above its equilibrium solubility, and the calculated electron–phonon coupling strength is found to be consistent with a conventional phonon-mediated coupling mechanism.
Abstract: Although the local resistivity of semiconducting silicon in its standard crystalline form can be changed by many orders of magnitude by doping with elements, superconductivity has so far never been achieved. Hybrid devices combining silicon's semiconducting properties and superconductivity have therefore remained largely underdeveloped. Here we report that superconductivity can be induced when boron is locally introduced into silicon at concentrations above its equilibrium solubility. For sufficiently high boron doping (typically 100 p.p.m.) silicon becomes metallic(1). We find that at a higher boron concentration of several per cent, achieved by gas immersion laser doping, silicon becomes superconducting. Electrical resistivity and magnetic susceptibility measurements show that boron-doped silicon (Si:B) made in this way is a superconductor below a transition temperature T-c approximate to 0.35 K, with a critical field of about 0.4 T. Ab initio calculations, corroborated by Raman measurements, strongly suggest that doping is substitutional. The calculated electron-phonon coupling strength is found to be consistent with a conventional phonon-mediated coupling mechanism(2). Our findings will facilitate the fabrication of new silicon-based superconducting nano-structures and mesoscopic devices with high-quality interfaces.

Journal ArticleDOI
He Hu1, Weihua Zhang1
TL;DR: In this article, a literature review aims to highlight recent advances in the synthesis of doped ZnS semiconductor nanoparticle materials and their wonderful properties, for example, the shift and broadening of spectrum, high luminescent quantum efficiency, shorting of emission lifetime and upconversion emission.

Journal ArticleDOI
TL;DR: In this paper, a method is proposed to optimize the light-scattering capacity of ZnO layers, and the incorporation of these layers as front transparent conductive oxides for p-i-n thin-film microcrystalline silicon solar cells is studied.

Journal ArticleDOI
TL;DR: In this article, a review of the field of magnetically doped oxides and nitrides is presented from a materials science perspective, focusing on films prepared not only by conventional vacuum deposition methods, but also by spin coating colloidal nanoparticles in air.

Journal ArticleDOI
TL;DR: In this article, the effect of Mn and Nb dopants on electric properties of BFO films was interpreted by defect chemistry and chemical reaction in the chemical solution deposition (CSD) process.
Abstract: Polycrystalline Mn-doped, Nb-doped, and pure BiFeO3 (BFO) films were fabricated via chemical solution deposition (CSD) method. Influence of Mn and Nb dopants on electric properties of BFO films were studied. The current density versus electric field (J-E) characteristics indicated that conduction mechanisms of Mn-doped, Nb-doped, and pure BFO films annealed at 500°C were Ohmic conduction, grain boundary limited conduction, and space charge limited conduction, respectively. The effect of Mn and Nb dopants on electric properties of BFO films was interpreted by defect chemistry and chemical reaction in the CSD process. The Nb dopant is effective in improving electrical properties of CSD-derived BFO films, while Mn is harmful in this respect.

Journal ArticleDOI
TL;DR: In this article, the structural properties of Ag-doped p-type ZnO thin films have been systematically characterized by observing the shift of (0002) peak to investigate the substitution of Ag+ for Zn+.
Abstract: p-type ZnO films have been fabricated on a (0001) Al2O3 substrate, using Ag2O as a silver dopant by pulsed laser deposition. The structural property of those films is systematically characterized by observing the shift of (0002) peak to investigate the substitution of Ag+ for Zn+. Narrow deposition temperature for Ag-doped p-type ZnO films has been obtained in the range of 200–250°C with the hole concentration of 4.9×1016–6.0×1017cm−3. A neutral acceptor bound exciton has been clearly observed by photoluminescence emitted at 3.317eV in Ag-doped p-type ZnO thin films.

Journal ArticleDOI
TL;DR: In this article, a two-component layered structure of organic light-emitting transistors (OLETs) with balanced ambipolar transport and mobility as large as 3 × 10 cm V s is presented.
Abstract: Today organic materials are routinely employed for the fabrication of light-emitting devices (OLEDs) and thin-film transistors (OTFTs), with the first technological realizations already having reached the market. Moreover, OTFTs with unipolar mobility values comparable to those of amorphous silicon (1 cm V s) have now been demonstrated. Applications impacting display technologies and those sectors where low cost is a key factor and low performance is acceptable include electronic paper and radio-frequency identification (RF-ID) products. In a recent development, OTFTs also exhibiting electroluminescence (EL) have been successfully demonstrated. Organic light-emitting transistors (OLETs) represent a significant technological advance by combining two functionalities, electrical switching and light emission, in a single device, thus significantly increasing the potential applications of organic semiconductors. In particular, if appropriate materials can be introduced, OLETs offer an ideal structure for improving the lifetime and efficiency of organic light-emitting heterostructures due to the intrinsically different driving conditions and charge-carrier balance compared to conventional OLEDs. Potential applications of OLETs include flat-panel display technologies, lighting, and, ultimately, easily fabricated organic lasers. The first OLET prototypes were unipolar transport devices, and recombination was expected to take place in close proximity to the metallic drain electrode where efficiency-depleting exciton quenching is also likely to occur. To avoid this significant device deficiency and to instead generate EL nearer the center of the channel, OLETs with ambipolar charge transport would be highly desirable. Furthermore, balanced ambipolar conduction is crucial for maximizing exciton recombination through efficient electron–hole balancing. Up to now various solutions have been proposed: single ambipolar materials and two-component coevaporated or layered structures. In coevaporated films, two materials are simultaneously sublimed to form bulk heterojunctions. However, carrier transport is unbalanced and the mobility values are below 10 cm V s. Devices employing a polymer film showing intrinsic ambipolar transport have also been reported but with mobility values for both charge carriers around 10 cm V s. In this paper we report OLETs based on two-component layered structures that have balanced ambipolar transport and mobility values as large as 3 × 10 cm V s. These devices are realized by sequentially depositing p-type (a,x-dihexyl-quaterthiophene, DH4T) and n-type films (N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide, PTCDIC13H27, P13). The combination with the highest mobility and most-balanced transport is obtained with DH4T grown in direct contact with the dielectric. For comparison, we have also employed pentacene in place of DH4T as the p-type material and showed that unbalanced ambipolarity is obtained. Morphological analysis of the outermost and buried layers, performed by laser scanning confocal microscopy (LSCM), allows selective imaging of materials with energetically separated photoluminescence (PL) spectra. Importantly, it is shown that ‘growth compatibility’ between the nand p-type materials is essential in forming a continuous interface and thereby controlling the resulting OLET optoelectronic-response properties. Each OLET material was first evaluated in a single layer in a top source–drain contact OTFT. As substrates we employed heavily doped silicon wafers with thermally grown oxides. Surface treatments such as octadecyltrichlorosilane or hexamethyldisilazane did not result in substantial improvement in the device performance. Parameters such as substrate temperature (Tsub) and evaporation rate were varied to optimize electrical characteristics. The optimum growth conditions were found to be: Tsub = 90 °C and rate = 0.1 A s –1 for DH4T, and Tsub = 25 °C and rate = 0.1 A s –1 for P13. In Table 1, the mobility (l) and threshold-voltage (Vth) values obtained are summarized. These are comparable to the highest values reported in the literature. The DH4T devices were stable even C O M M U N IC A TI O N S

Journal ArticleDOI
TL;DR: The synthesis and characterization of cobalt-doped zinc oxide (Zn1 xCoxO) nanowires grown by a solution-phase synthesis is presented, which allows for the doping of different transition metals (e.g., Mn, Fe, Cu).
Abstract: The introduction of impurity atoms into semiconducting materials is the primary method for controlling the properties of the semiconductor, such as band gap or electrical conductivity. This practice is routinely performed with bulk semiconductors and, more recently, has been extended to nanoscale semiconductors as well. In particular, II–VI and III–V semiconductors that have been doped with transition metals are currently generating much research interest, principally for their novel magnetic properties. These semiconductors are commonly called dilute magnetic semiconductors and are envisioned to be potential building blocks for spintronic devices. One such material is transition-metal doped zinc oxide (Zn1 xMxO), which has been theoretically predicted to be ferromagnetic at room temperature. 2] Although this system has been under experimental study for some time, the vast majority of research conducted on this material has been done on bulk crystals or thin films. There are very few reports on the fabrication of one-dimensional nanostructures of Zn1 xMxO, and high-temperature, vapor-phase methods are employed in the syntheses. Although this approach has proven quite effective for the production of a multitude of nanoscale semiconductors, gas-phase syntheses are considerably limited in regards to homogeneous doping and alloying because of high-growth temperatures. Solution-based synthetic schemes possess inherent advantages in the above areas over vapor-phase routes, in addition to ecological benefits. Whereas there have been several reports on the synthesis of pure ZnO nanowires from the solution phase, the only solution-based methods for the production of Zn1 xMxO yield isotropic quantum dots, such as those reported by Gamelin et al. To date, no reports of anisotropic, transition-metal doped ZnO nanowires grown from the solution phase exist. We present herein the synthesis and characterization of cobalt-doped zinc oxide (Zn1 xCoxO) nanowires grown by a solution-phase synthesis. The synthetic process presented herein also allows for the doping of different transition metals (e.g., Mn, Fe, Cu); however, this report is limited to the cobalt-doped system. The nanowires were synthesized by the thermal decomposition of zinc acetate and cobalt(ii) acetate in refluxing trioctylamine (see the Experimental Section). Figure 1 shows

Journal ArticleDOI
TL;DR: Li-doped, p-type ZnO thin films have been realized via dc reactive magnetron sputtering in this article, and an optimized result with a resistivity of 16.4Ωcm, Hall mobility of 2.65cm2∕Vs, and hole concentration of 1.44×1017cm−3 was achieved, and electrically stable over a month.
Abstract: Li-doped, p-type ZnO thin films have been realized via dc reactive magnetron sputtering. An optimized result with a resistivity of 16.4Ωcm, Hall mobility of 2.65cm2∕Vs, and hole concentration of 1.44×1017cm−3 was achieved, and electrically stable over a month. Hall-effect measurements supported by secondary ion mass spectroscopy indicated that the substrate temperature played a key role in optimizing the p-type conduction of Li-doped ZnO thin films. Furthermore, ZnO-based p-n homojunction was fabricated by deposition of a Li-doped p-type ZnO layer on an Al-doped n-type ZnO layer.

Journal ArticleDOI
09 Feb 2006-Nature
TL;DR: It is shown—using scanning tunnelling microscopy, electronic transport measurements, and theory—that electronic conduction in thin SOI(001) is determined not by bulk dopants but by the interaction of surface or interface electronic energy levels with the ‘bulk’ band structure of the thin silicon template layer, which enables high-mobility carrier conductionIn nanometre-scale SOI.
Abstract: The widely used ‘silicon-on-insulator’ (SOI) system consists of a layer of single-crystalline silicon supported on a silicon dioxide substrate. When this silicon layer (the template layer) is very thin, the assumption that an effectively infinite number of atoms contributes to its physical properties no longer applies, and new electronic, mechanical and thermodynamic phenomena arise1,2,3,4, distinct from those of bulk silicon. The development of unusual electronic properties with decreasing layer thickness is particularly important for silicon microelectronic devices, in which (001)-oriented SOI is often used5,6,7. Here we show—using scanning tunnelling microscopy, electronic transport measurements, and theory—that electronic conduction in thin SOI(001) is determined not by bulk dopants but by the interaction of surface or interface electronic energy levels with the ‘bulk’ band structure of the thin silicon template layer. This interaction enables high-mobility carrier conduction in nanometre-scale SOI; conduction in even the thinnest membranes or layers of Si(001) is therefore possible, independent of any considerations of bulk doping, provided that the proper surface or interface states are available to enable the thermal excitation of ‘bulk’ carriers in the silicon layer.

Journal ArticleDOI
TL;DR: Magneto-optic studies of ZnO doped with transition metals Co, Mn, V, and Ti indicate a significant magnetic circular dichroism (MCD) at theZnO band edge at room temperature, together with an associated dispersive Faraday rotation.
Abstract: Magneto-optic studies of ZnO doped with transition metals Co, Mn, V, and Ti indicate a significant magnetic circular dichroism (MCD) at the ZnO band edge at room temperature, together with an associated dispersive Faraday rotation. Similar spectra occur for each dopant, which implies that the ferromagnetism is an intrinsic property of the bulk ZnO lattice. At 10 K, additional paramagnetic contributions to the MCD are observed, but above about 150 K, the magnitude of the MCD signal is dominated by the ferromagnetism and is almost temperature independent. The MCD at the ZnO band edge shows room temperature hysteretic behavior.