Showing papers on "Doping published in 2004"

Repeated temperature modulation epitaxy for p-type doping and light-emitting diode based on ZnO

Abstract: Since the successful demonstration of a blue light-emitting diode (LED)1, potential materials for making short-wavelength LEDs and diode lasers have been attracting increasing interest as the demands for display, illumination and information storage grow2,3,4. Zinc oxide has substantial advantages including large exciton binding energy, as demonstrated by efficient excitonic lasing on optical excitation5,6. Several groups have postulated the use of p-type ZnO doped with nitrogen, arsenic or phosphorus7,8,9,10, and even p–n junctions11,12,13. However, the choice of dopant and growth technique remains controversial and the reliability of p-type ZnO is still under debate14. If ZnO is ever to produce long-lasting and robust devices, the quality of epitaxial layers has to be improved as has been the protocol in other compound semiconductors15. Here we report high-quality undoped films with electron mobility exceeding that in the bulk. We have used a new technique to fabricate p-type ZnO reproducibly. Violet electroluminescence from homostructural p–i–n junctions is demonstrated at room-temperature.

Nano-network electronic conduction in iron and nickel olivine phosphates.

Abstract: The provision of efficient electron and ion transport is a critical issue in an exciting new group of materials based on lithium metal phosphates that are important as cathodes for lithium-ion batteries. Much interest centres on olivine-type LiFePO(4), the most prominent member of this family. Whereas the one-dimensional lithium-ion mobility in this framework is high, the electronically insulating phosphate groups that benefit the voltage also isolate the redox centres within the lattice. The pristine compound is a very poor conductor (sigma approximately 10(-9) S cm(-1)), thus limiting its electrochemical response. One approach to overcome this is to include conductive phases, increasing its capacity to near-theoretical values. There have also been attempts to alter the inherent conductivity of the lattice by doping it with a supervalent ion. Compositions were reported to be black p-type semiconductors with conductivities of approximately 10(-2) S cm(-1) arising from minority Fe(3+) hole carriers. Our results for doped (and undoped) LiMPO(4) (M = Fe, Ni) show that a percolating nano-network of metal-rich phosphides are responsible for the enhanced conductivity. We believe our demonstration of non-carbonaceous-network grain-boundary conduction to be the first in these materials, and that it holds promise for other insulating phosphates.

Superconductivity in diamond

Abstract: Diamond is an electrical insulator well known for its exceptional hardness. It also conducts heat even more effectively than copper, and can withstand very high electric fields1. With these physical properties, diamond is attractive for electronic applications2, particularly when charge carriers are introduced (by chemical doping) into the system. Boron has one less electron than carbon and, because of its small atomic radius, boron is relatively easily incorporated into diamond3; as boron acts as a charge acceptor, the resulting diamond is effectively hole-doped. Here we report the discovery of superconductivity in boron-doped diamond synthesized at high pressure (nearly 100,000 atmospheres) and temperature (2,500–2,800 K). Electrical resistivity, magnetic susceptibility, specific heat and field-dependent resistance measurements show that boron-doped diamond is a bulk, type-II superconductor below the superconducting transition temperature Tc ≈ 4 K; superconductivity survives in a magnetic field up to Hc2(0) ≥ 3.5 T. The discovery of superconductivity in diamond-structured carbon suggests that Si and Ge, which also form in the diamond structure, may similarly exhibit superconductivity under the appropriate conditions.

Disordered zinc in Zn4Sb3 with phonon-glass and electron-crystal thermoelectric properties.

Abstract: By converting waste heat into electricity, thermoelectric generators could be an important part of the solution to today's energy challenges. The compound Zn_4Sb_3 is one of the most efficient thermoelectric materials known. Its high efficiency results from an extraordinarily low thermal conductivity in conjunction with the electronic structure of a heavily doped semiconductor. Previous structural studies have been unable to explain this unusual combination of properties. Here, we show through a comprehensive structural analysis using single-crystal X-ray and powder-synchrotron-radiation diffraction methods, that both the electronic and thermal properties of Zn_4Sb_3 can be understood in terms of unique structural features that have been previously overlooked. The identification of Sb^(3-) ions and Sb_2^(4-) dimers reveals that Zn_4Sb_3 is a valence semiconductor with the ideal stoichiometry Zn_(13)Sb_(10). In addition, the structure contains significant disorder, with zinc atoms distributed over multiple positions. The discovery of glass-like interstitial sites uncovers a highly effective mechanism for reducing thermal conductivity. Thus Zn_4Sb_3 is in many ways an ideal 'phonon glass, electron crystal' thermoelectric material.

Semiconductor device, its manufacturing method, and electronic device

Abstract: A thin film transistor (1) wherein a gate electrode (3) is formed on an insulative substrate (2), a gate insulating layer (4) is formed on the gate electrode (3), a semiconductor layer (5) is formed on the gate insulating layer (4), a source electrode (6) and a drain electrode (7) are formed on the semiconductor layer (5), and a protective layer (8) covering them are formed. The semiconductor layer (5) is isolated from the atmosphere. The semiconductor layer (5) (active layer) is formed of a ZnO polycrystalline semiconductor doped with, for example, a group V element. Since the surface state of the ZnO semiconductor is reduced thanks to the protective layer (8) and inward expansion of the depletion layer is prevented, the ZnO semiconductor is of an n-type showing its intrinsic resistance value and contains excessive free electrons. The added element acts as acceptor impurities in the ZnO semiconductor, decreasing the excessive electrons. Thus the gate voltage to eliminate the excessive free electrons lowers, thereby making the threshold voltage around 0 V. A semiconductor device using a zinc oxide for an active layer and having a protective layer for isolating the active layer from the atmosphere can be actually used.

Doping by large-size-mismatched impurities: the microscopic origin of arsenic- or antimony-doped p-type zinc oxide.

Abstract: Based on first-principles calculations, a model for large-size-mismatched group-V dopants in ZnO is proposed. The dopants do not occupy the O sites as is widely perceived, but rather the Zn sites: each forms a complex with two spontaneously induced Zn vacancies in a process that involves fivefold As coordination. Moreover, an As(Zn)-2V(Zn) complex may have lower formation energy than any of the parent defects. Our model agrees with the recent observations that both As and Sb have low acceptor-ionization energies and that to obtain p-type ZnO requires O-rich growth or annealing conditions.

N-Doping Of Organic Semiconductors

Abstract: The invention relates to a process for producing doped organic semiconductor materials with an elevated charge carrier density and effective charge carrier mobility by doping, in which the doping agent is substantially produced by electrocrystallization in a first step, the doping agent is selected from a group of organic compounds with a low oxidation potential, and in which an organic semiconductor material is doped with the doping agent in a second step. Furthermore, the invention relates to doped organic semiconductor materials with an elevated charge carrier density and effective charge carrier mobility produced by the aforementioned process. Furthermore, the invention relates to an organic diode comprising doped organic semiconductor materials produced in accordance with the aforementioned process.

Growth and transport properties of complementary germanium nanowire field-effect transistors

Abstract: n- and p-type Ge nanowires were synthesized by a multistep process in which axial elongation, via vapor–liquid–solid (VLS) growth, and doping were accomplished in separate chemical vapor deposition steps. Intrinsic, single-crystal, Ge nanowires prepared by Au nanocluster-mediated VLS growth were surface-doped in situ using diborane or phosphine, and then radial growth of an epitaxial Ge shell was used to cap the dopant layer. Field-effect transistors prepared from these Ge nanowires exhibited on currents and transconductances up to 850 μA/μm and 4.9 μA/V, respectively, with device yields of >85%.

The Effect of Nitrogen Ion Implantation on the Photoactivity of TiO2 Rutile Single Crystals

Abstract: The effect of impurity doping on the photoactivity of TiO2 rutile single crystals was subjected to a combined surface-science and bulk-analysis study. The incorporation of nitrogen ions, N-, into TiO2 single crystals was achieved by sputtering with N2+/Ar+ mixtures and subsequent annealing to 900 K under ultrahigh vacuum conditions. This procedure leads to a 90 A thick structurally modified near-surface region, which, by the use of cross sectional transmission electron microscopy, can be described as rutile grains imbedded within a monocrystalline strained rutile matrix. The presence of N- ions distributed in the first 200 A below the surface was revealed by X-ray photoelectron spectroscopy, in agreement with sputter depth profiles obtained by secondary ion mass spectroscopy. The concentration of N- doping is about 1020 cm-3 in the first 200 A of the near-surface region. The photodesorption of O2 was employed to study the changes in the photochemical properties of nitrogen-implanted crystals. The action c...

How To Make Ohmic Contacts to Organic Semiconductors

Abstract: The process of charge injection plays an important role in organic semiconductor devices. We review various experimental techniques that allow injection to be separated from other competing processes, and quantify the injection efficiency of a contact. We discuss the dependence of the injection efficiency on parameters such as the energy barrier at the interface, the carrier mobility of the organic semiconductor, its carrier density (doping level), the presence of mobile ions, and the sample geometry. Based on these findings, we outline guidelines for forming ohmic contacts and present examples of contact engineering in organic semiconductor devices.

Infrared absorption by sulfur-doped silicon formed by femtosecond laser irradiation

Abstract: We microstructured silicon surfaces with femtosecond laser irradiation in the presence of SF6. These surfaces display strong absorption of infrared radiation at energies below the band gap of crystalline silicon. We report the dependence of this below-band gap absorption on microstructuring conditions (laser fluence, number of laser pulses, and background pressure of SF6) along with structural and chemical characterization of the material. Significant amounts of sulfur are incorporated into the silicon over a wide range of microstructuring conditions; the sulfur is embedded in a disordered nanocrystalline layer less than 1 μm thick that covers the microstructures. The most likely mechanism for the below-band gap absorption is the formation of a band of sulfur impurity states overlapping the silicon band edge, reducing the band gap from 1.1 eV to approximately 0.4 eV.

Blueshift of near band edge emission in Mg doped ZnO thin films and aging

Abstract: Pure and Mg doped ZnO thin films were deposited at 400 °C on glass substrates by pulsed laser deposition. An x-ray diffractometer (XRD) was used to investigate the structural properties of the thin films. It is found that all the thin films have a preferred (002) orientation. The peak position of (002) orientation is found to shift from 34.39° to 34.55°. The lattice constants of ZnO thin films were also obtained from XRD data. It is found that, with the increase of the dopant concentration, the lattice constant a decreases from 3.25 to 3.23 A, and c decreases from 5.20 to 5.16 A. From the spectrophotometer transmittance data, the band gap energies of the thin films were calculated by a linear fitting process. The band gap energy of Mg doped ZnO thin film increases with increasing dopant concentration. In photoluminescence (PL) spectra, two PL emission peaks are found in pure ZnO thin films, one is the near band edge (NBE) emission at 3.28 eV, and the other is green-yellow-red emission at around 2.4 eV. However, with the increase of the dopants, no green-yellow-red emissions are found in PL of Mg doped ZnO thin films. The NBE emission has a blueshift compared with that of pure ZnO thin film (as much as 0.12 eV). As time goes on, NBE emission in pure ZnO thin film is enhanced, and the green-yellow-red emissions disappear.

Efforts to improve carrier mobility in radio frequency sputtered aluminum doped zinc oxide films

Abstract: This study addresses the electrical and optical properties of radio frequency magnetron sputtered aluminum doped zinc oxide (ZnO:Al) films. The main focus was on the improvement in carrier mobility μ to achieve simultaneously high transparency for visible and particularly near-infrared light and low resistivity. The influence of Al concentration in the target, film thickness, sputter power, deposition pressure, and substrate temperature on material properties was investigated. The structural, compositional, electrical and optical properties were studied using x-ray diffraction, secondary ion mass spectrometry (SIMS), room temperature Hall effect measurements and spectral photometry, respectively. All ZnO:Al films were polycrystalline and preferentially oriented along [002]. The grain size along the direction of growth increased with higher Al doping and with increasing film thickness. The SIMS measurements revealed that the Al concentration in the film was nearly the same as in the target. Carrier concent...

Glass-based soi structures

Abstract: Semiconductor-on-insulator (SOI) structures, including large area SOI structures, are provided which have one or more regions composed of a layer (15) of a substantially single-crystal semiconductor (e.g., doped silicon) attached to a support substrate (20) composed of an oxide glass or an oxide glass-ceramic. The oxide glass or oxide glass-ceramic is preferably transparent and preferably has a strain point of less than 1000°C, a resistivity at 250°C that is less than or equal to 1016 -cm, and contains positive ions (e.g., alkali or alkaline-earth ions) which can move within the glass or glass-ceramic in response to an electric field at elevated temperatures (e.g., 300 - 1000°C). The bond strength between the semiconductor layer (15) and the support substrate (20) is preferably at least 8 joules/meter2. The semiconductor layer (15) can include a hybrid region (16) in which the semiconductor material has reacted with oxygen ions originating from the glass or glass-ceramic. The support substrate (20) preferably includes a depletion region (23) which has a reduced concentration of the mobile positive ions.

Field emission from gallium-doped zinc oxide nanofiber array

Abstract: Gallium-doped nanostructural zinc oxide fibers have been fabricated by vapor-phase transport method of heating the mixture of zinc oxide, gallium oxide, and graphite powders in air. The zinc oxide fibers grew along [002] direction, forming a vertically aligned array that is predominantly perpendicular to the substrate surface. With a gallium doping concentration of 0.73 at. %, the corresponding carrier concentration and resistivity were 3.77×1020 cm−3 and 8.9×10−4 Ω cm, respectively. The field emission of these vertically aligned ZnO fiber arrays showed a low field emission threshold (2.4 V/μm at a current density of 0.1 μA/cm2), high current density, and high field enhancement factor (2317). The dependence of emission current density on the electric field followed Fowler–Nordheim relationship. The enhanced field emission is attributed to the aligned structure, good crystal quality, and especially, the improved electrical properties (increased conductivity and reduced work function) of the nanofibers due ...

Band gap energy of pure and Al-doped ZnO thin films

Abstract: Pulsed laser deposition (PLD) technique is used to deposit pure and Al-doped ZnO thin films at different temperatures on glass substrates. From the transmission data from optical spectroscopy the band gap energy Eg of the films is derived. The dependences of Eg on the deposition temperatures of the pure and Al-doped ZnO films are different. The band gap energy of the pure ZnO increases and saturates with temperature. However, Eg of Al-doped ZnO shows an exponential decrease. Refractive indices of 1.9–2.1 in the VIS are determined by the spectroscopic ellipsometry (SE). Photoluminescence (PL) data reveal the strong near band emission by increasing the deposition temperature. # 2003 Elsevier Ltd. All rights reserved.

Iron detection in crystalline silicon by carrier lifetime measurements for arbitrary injection and doping

Abstract: This work has been supported by NOVEM (The Netherlands Agency for Energy and the Environment) under contract no. 2020.01.13.11.2002.

Surface transfer doping of diamond

Abstract: The electronic properties of many materials can be controlled by introducing appropriate impurities into the bulk crystal lattice in a process known as doping. In this way, diamond (a well-known insulator) can be transformed into a semiconductor1, and recent progress in thin-film diamond synthesis has sparked interest in the potential applications of semiconducting diamond2,3. However, the high dopant activation energies (in excess of 0.36 eV) and the limitation of donor incorporation to (111) growth facets only have hampered the development of diamond-based devices. Here we report a doping mechanism for diamond, using a method that does not require the introduction of foreign atoms into the diamond lattice. Instead, C60 molecules are evaporated onto the hydrogen-terminated diamond surface, where they induce a subsurface hole accumulation and a significant rise in two-dimensional conductivity. Our observations bear a resemblance to the so-called surface conductivity of diamond4,5,6,7,8 seen when hydrogenated diamond surfaces are exposed to air, and support an electrochemical model in which the reduction of hydrated protons in an aqueous surface layer gives rise to a hole accumulation layer6,7. We expect that transfer doping by C60 will open a broad vista of possible semiconductor applications for diamond.

Vertical memory device structures

Abstract: Vertically oriented semiconductor memory cells are added to a separately fabricated substrate that includes electrical devices and/or interconnect. The plurality of vertically oriented semiconductor memory cells are physically separated from each other, and are not disposed within the same semiconductor body. The plurality of vertically oriented semiconductor memory cells can be added to the separately fabricated substrate as a thin layer including several doped semiconductor regions which, subsequent to attachment, are etched to produce individual doped stack structures, which are then supplied with various dielectric coatings, gate electrodes, and contacts by means of further processing operations. Alternatively, the plurality of vertically oriented semiconductor memory cells may be completely fabricated prior to attachment. DRAMs, SRAMs, non-volatile memories, and combinations of memory types can be provided.

Semiconductor device and method of manufacturing the same

Abstract: PROBLEM TO BE SOLVED: To provide a bipolar transistor of a self-aligned structure which has an improved current gain cut-off frequency and maximum transmission frequency, and to provide a method of manufacturing the transistor SOLUTION: The bipolar transistor in made to have a structure where a polycrystalline silicon doped with an impurity of a second conduction type is buried in an external base polycrystalline silicon in the vicinity of an emitter at a position of the lower part of the external base polycrystalline silicon adjacent to an epitaxial base layer After an insulating film of the lower part of the external base polycrystalline silicon is etched to form a recess, a polycrystalline silicon layer doped with the impurity of the second conduction type is formed, and then etched back to leave the polycrystalline silicon only in the recess, thus obtainable the bipolar transistor COPYRIGHT: (C)2005,JPO&NCIPI

Kelvin Probe Study of Band Bending at Organic Semiconductor/Metal Interfaces: Examination of Fermi Level Alignment

Abstract: Band bending is a fundamental issue for discussing organic devices. Band bending with Fermi level alignment between semiconductors and metals are often assumed, although the validity of this scheme in the case of organic semiconductors has been not yet established. In this paper, our recent efforts to examine band bending in organic semiconductors using Kelvin probe method (KPM) are reported. After discussing the applicability of KPM to organic thick film – metal substrate system, the results for C60, TPD, and Alq3 are shown to discuss band bending of the films without intentional doping in ultrahigh vacuum condition. Gradual band bending was observed for C60/metal interfaces although the width of the space charge layer is in the order of 100 nm. In contrast, flat band feature was observed for TPD/metal interfaces probably because of its high purity. These results demonstrate that the frame work of band bending used in inorganic semiconductor interfaces is still valid for organic semiconductors although much thicker films are often necessary to achieve bulk Fermi level alignment. For Alq3/metal interfaces formed in dark condition, we found a new type of band bending where the energy levels change as a linear function of the distance from the interface. The observed location of the vacuum level was far below the Fermi level of the metal substrates, clearly indicating that Fermi level varies place by place in the system. Such electronically non-equilibrium state was quite stable for the order of years. The concept of Fermi level alignment is also discussed in relation to the observed energy diagrams. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Possible p-type doping with group-I elements in ZnO

Abstract: Based on first-principles calculations, we suggest a method for fabricating $p$-type ZnO with group-I elements such as Li and Na. With group-I dopants alone, substitutional acceptors are mostly self-compensated by interstitial donors. In ZnO codoped with H impurities, the formation of compensating interstitials is severely suppressed, and the acceptor solubility is greatly enhanced by forming H-acceptor complexes. The H atoms can be easily dissociated from these defect complexes at relatively low annealing temperatures, and thus low-resistivity $p$-type ZnO is achievable with dopants different from group-V elements.

Improved photocatalytic activity of Sn4+ doped TiO2 nanoparticulate films prepared by plasma-enhanced chemical vapor deposition

Abstract: Sn4+ ion doped TiO2 (TiO2–Sn4+) nanoparticulate films with a doping ratio of about 7∶100 [(Sn)∶(Ti)] were prepared by the plasma-enhanced chemical vapor deposition (PCVD) method. The doping mode (lattice Ti substituted by Sn4+ ions) and the doping energy level of Sn4+ were determined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), surface photovoltage spectroscopy (SPS) and electric field induced surface photovoltage spectroscopy (EFISPS). It is found that the introduction of a doping energy level of Sn4+ ions is profitable to the separation of photogenerated carriers under both UV and visible light excitation. Characterization of the films with XRD and SPS indicates that after doping by Sn, more surface defects are present on the surface. Consequently, the photocatalytic activity for photodegradation of phenol in the presence of the TiO2–Sn4+ film is higher than that of the pure TiO2 film under both UV and visible light irradiation.

Three-dimensional MgB2-type superconductivity in hole-doped diamond.

Abstract: We substantiate by numerical and analytical calculations that the recently discovered superconductivity below 4 K in 3% boron-doped diamond is caused by electron-phonon coupling of the same type as in MgB2, albeit in three dimensions. Holes at the top of the zone-centered, degenerate sigma-bonding valence-band couple strongly to the optical bond-stretching modes. The increase from two to three dimensions reduces the mode softening crucial for T(c) reaching 40 K in MgB2. Even if diamond had the same bare coupling constant as MgB2, which could be achieved with 10% doping, T(c) would be only 25 K. Superconductivity above 1 K in Si (Ge) requires hole doping beyond 5% (10%).

Room-temperature ferromagnetic nanotubes controlled by electron or hole doping

Abstract: Nanotubes and nanowires with both elemental1,2 (carbon or silicon) and multi-element3,4,5 compositions (such as compound semiconductors or oxides), and exhibiting electronic properties ranging from metallic to semiconducting, are being extensively investigated for use in device structures designed to control electron charge6,7,8. However, another important degree of freedom—electron spin, the control of which underlies the operation of ‘spintronic’ devices9—has been much less explored. This is probably due to the relative paucity of nanometre-scale ferromagnetic building blocks10 (in which electron spins are naturally aligned) from which spin-polarized electrons can be injected. Here we describe nanotubes of vanadium oxide (VOx), formed by controllable self-assembly11, that are ferromagnetic at room temperature. The as-formed nanotubes are transformed from spin-frustrated semiconductors to ferromagnets by doping with either electrons or holes, potentially offering a route to spin control12 in nanotube-based heterostructures13.

Above-room-temperature ferromagnetic Ni2+-doped ZnO thin films prepared from colloidal diluted magnetic semiconductor quantum dots

Abstract: We report the preparation of spin-coated nickel-doped zinc oxide nanocrystalline thin films using high-quality colloidal diluted magnetic semiconductor (DMS) quantum dots as solution precursors. These films show robust ferromagnetism with Curie temperatures above 350K and 300K saturation moments up to 0.1Bohr magnetons per nickel. These results demonstrate a step toward the use of colloidal zero-dimensional DMS nanocrystals as building blocks for the bottom-up construction of more complex ferromagnetic semiconductor nanostructures.

Three-dimensional integrated circuit structure and method of making same

Abstract: Vertically oriented semiconductor devices may be added to a separately fabricated substrate that includes electrical devices and/or interconnect The plurality of vertically oriented semiconductor devices are physically separated from each other, and are not disposed within the same semiconductor body, or semiconductor substrate The plurality of vertically oriented semiconductor devices may be added to the separately fabricated substrate as a thin layer including several doped semiconductor regions which, subsequent to attachment, are etched to produce individual doped stack structures Alternatively, the plurality of vertically oriented semiconductor devices may be fabricated prior to attachment to the separately fabricated substrate The doped stack structures may form the basis for diodes, capacitors, n-MOSFETs, p-MOSFETs, bipolar transistors, and floating gate transistors Ferroelectric memory devices, Ferromagnetic memory devices, chalcogenide phase change devices, may be formed in a stackable add-on layer for use in conjunction with a separately fabricated substrate Stackable add-on layers may include interconnect lines

Strong Room-Temperature Ferromagnetism in Co2+-Doped TiO2 Made from Colloidal Nanocrystals

Abstract: Colloidal cobalt-doped TiO2 (anatase) nanocrystals were synthesized and studied by electronic absorption, magnetic circular dichroism, transmission electron microscopy, magnetic susceptibility, cobalt K-shell X-ray absorption spectroscopy, and extended X-ray absorption fine structure measurements. The nanocrystals were paramagnetic when isolated by surface-passivating ligands, weakly ferromagnetic (Ms ≈ 1.5 × 10-3 μB/Co2+ at 300 K) when aggregated, and strongly ferromagnetic (up to Ms = 1.9 μB/Co2+ at 300 K) when spin-coated into nanocrystalline films. X-ray absorption data reveal that cobalt is in the Co2+ oxidation state in all samples. In addition to providing strong experimental support for the existence of intrinsic ferromagnetism in cobalt-doped TiO2, these results demonstrate the possibility of using colloidal TiO2 diluted magnetic semiconductor nanocrystals as building blocks for assembly of ferromagnetic semiconductor nanostructures with potential spintronics applications.