Electrical Properties Of Junctions Research Articles

Strong ultraviolet emission and rectifying behavior of nanocrystalline ZnO films

Abstract Nanocrystalline ZnO thin films on p-type Si(1 0 0) substrates have been prepared by a sol-gel method. X-ray diffraction results showed polycrystalline wurtzite with a preferential (0 0 2) orientation. Morphology studies revealed that the films consisted of uniform grains in size of ∼33 nm. A strong ultraviolet emission with no distinct visible emissions was observed in room temperature photoluminescence spectrum. The ultraviolet emission results from the recombination of free exciton with stronger longitudinal optical (LO) phonon replica. Stronger LO phonon replica may be ascribed to the strong interaction between the exciton and LO phonon in nanostructure. Nanostructure of films is also responsible for the blueshift of free exciton emission compared with single-crystal ZnO. The absence of E 1 (LO) mode in Raman spectrum further confirmed low defect density in as-grown nanocrystalline ZnO films. The electrical junction properties characterized by current–voltage measurement showed a rectifying behavior.

Characterization of n-ZnO/p-Si films grown by magnetron sputtering

ZnO films were deposited by RF magnetron sputtering on single p-Si substrates to form n-ZnO/p-Si heterojunctions. Various substrate temperatures of 25, 100, 200, 300 and 400 ∘C were used. The electrical junction properties were characterized by current–voltage ( I – V ) and capacitance–voltage ( C – V ) methods. Calculations of the barrier height from classical 1 / C 2 – V characterizations and from the I – V in dark conditions indicate merely the same values of 0.7 eV. Moreover, the optical spectra showed that the reflectance of the ZnO films grown with different substrate temperatures is inferior to that of bare silicon substrate in the UV and visible region. The smallest reflectance in the visible region was found for films grown at higher substrate temperature, indicating a possible application of these films as anti-reflection coatings for Si-based optoelectronic devices allowing the minimization of reflection losses.

Electrical properties of junction between aluminium and poly(aniline)–poly(vinyl chloride) composite

Schottky barrier diode based on composite of polyaniline with polyvinyl chloride has been fabricated and characterized using aluminium as Schottky contact and platinum as an Ohmic contact. Current–voltage ( I– V) plots were non-linear and capacitance–voltage ( C– V) plots were almost linear in reverse bias indicating rectification behavior. The observed current–voltage characteristics can be satisfactorily fitted using the modified Schottky equation. Various junction parameters were calculated from the temperature-dependent I– V and C– V data and discussed. These results indicate that the composite materials have better mechanical strength and diode quality compared to that of pure polymer.

Structure and characteristics of ZnO:Al/n-Si heterojunctions prepared by magnetron sputtering

Aluminium-doped zinc oxide (ZnO:Al) films were deposited by RF magnetron sputtering on single-crystal n-Si substrates to form ZnO:Al/n-Si heterojunctions. The structure of the ZnO:Al films was analysed by X-ray diffraction spectroscopy and scanning electron microscopy. The structural properties of the ZnO:Al/n-Si junction were studied by transmission electron microscopy. The electrical junction properties were characterised by current–voltage ( I– V) and capacitance–voltage ( C– V) methods. The conductance measured shows a room-temperature turn-on voltage of 0.2–0.4 V. The ideality factor and the junction built-in potential deduced from I– V and C– V plots are 1.62 and 0.56 V at room temperature, respectively. Temperature-dependent dark forward current vs. voltage measurements suggest that trap-assisted multistep tunnelling is the dominant carrier transport mechanism in this heterojunction.

Symmetrical high-T c superconducting bicrystal Josephson junctions: Dependence of the electrical properties on the misorientation angle

The electrical properties of junctions at symmetrical bicrystal boundaries in high-T c superconducting films are studied as functions of the misorientation angle in the range 8°–45°. The junctions are prepared by growing YBa2Cu3O7 (YBCO) epitaxial films on Y-ZrO2 (YSZ) bicrystal substrates. The proportional relationship between the characteristic voltages and the normal conductivities of junctions is derived from the dependences of the critical current and the normal resistance on the misorientation angle. The results are interpreted within the model of a superconductor-dielectric with defect levels in the band gap of the superconductor. The deviations from the proportional relationship are explained by the junction inhomogeneity. The thickness of the effective dielectric layer in the bicrystal junction and the Bohr radius of electrons on the defects are estimated.

Electrochemical formation of GaAs/Bi Schottky barriers

Bismuth layers have been deposited electrochemically on (100) n- and p-type GaAs. The electrical properties of junctions on n-GaAs were dependent on the bismuth deposition potential. Bismuth films deposited at −0.2 V (Ag/AgCl) were compact, continuous, and exhibited good adhesion; the n-GaAs/Bi junctions exhibited an average barrier height of 0.83 eV. Films deposited at ⩽−0.3 V were porous and the barrier heights exhibited an aging effect decreasing to 0.73 eV after several days under ambient conditions. Bismuth films deposited on p-GaAs exhibited barrier heights of 0.57 eV. The sum of the barrier heights for n- and p-type junctions correspond to 1.40 eV, close to the band gap of GaAs consistent with Fermi-level pinning.

Electrical properties of covalently linked silicon/polypyrrole junctions

Electrodeposited polypyrrole films were formed on chemically modified hydrogen-terminated silicon surfaces that expose tethered pyrrole units. Semiconductor/polypyrrole junctions on the native and modified substrates exhibit diode-like characteristics, with those on the latter substrate exhibiting higher current densities and better ideality factors. Impedance measurements revealed that the improved electrical properties of junctions on the modified substrates were not due to a change in barrier height but rather a consequence of incorporating sites on the silicon surface where the polymer and semiconductor have direct contact.

Electrical Properties of Junctions between Electrodeposited Magnesium Phthalocyanine and Aluminum

2,9,16,23-Tetracarboxyphthalocyaninatomagnesium(II) [Mg(II)-taPc] films were obtained on indium/tin oxide (ITO) coated glass electrodes by electrodeposition, using MgCl2, CaCl2, CoCl2, or ZnCl2 as a supporting electrolyte. The electrical properties of junctions between electrodeposited Mg(II)-taPc film and aluminum electrode were evaluated by current-voltage measurements. The diode based on Mg(II)-taPc film containing Mg2+ as a bridging metal ion exhibited Zener-type breakdown, while the diode based on Mg(II)-taPc film containing Ca2+ or Zn2+ as a bridging metal ion showed almost symmetrical I–V. The diode based on Mg(II)-taPc film containing Co2+ as a bridging metal ion was electrically unstable. The diode based on Mg(II)-taPc film containing Mg2+, Ca2+, or Zn2+ as a bridging metal ion exhibited a photocurrent on forward biased condition.

The electrical properties of junctions between aluminium and doped polypyrrole

Polypyrrole (PPy) doped with small anions like or large polymeric anions such as poly(styrenesulphonate) forms a conducting organic solid. The electrical properties of metal contacts to this material were evaluated by current - voltage characteristics and impedance spectroscopy measurements. The I - V characteristics of the -doped device was symmetrical but non-ohmic, while that of the -doped diode was rectifying. The complex impedance spectra of -doped structures showed two partially overlapping semi-circles, which revealed the existence of two distinct regions at the metal/doped PPy junctions. They were modelled by an equivalent circuit consisting of two parallel RC circuits in series representing a thin insulating interfacial layer and a depletion region. The impedance spectra of -doped devices manifested a single semi-circle whose diameter depended on the bias voltage. In this case, the thin interfacial non-conducting layer was absent.

Effect of chemical and ion-beam etching on the atomic structure of interfaces in YBa2Cu3O7/PrBa2Cu3O7 Josephson junctions

The atomic structure of the interfaces of Josephson junctions formed by epitaxial YBa2Cu3O7/PrBa2Cu3O7/YBa2Cu3O7 triple-layer films was investigated by high-resolution transmission electron microscopy. The samples were fabricated by sputter deposition on surfaces which were etched ex situ either chemically, using a nonaqueous Br-ethanol solution, or by an Ar ion beam. In the interfaces produced after ion etching a thin intermediate layer with a thickness of a few nanometers was observed. The main part of this layer consists of cubic PrBa2Cu3O7 or YBa2Cu3O7 which is cation disordered. The interfaces formed during deposition on Br-ethanol-etched surfaces did not contain such an intermediate layer but exhibited high structural perfection similar to that of interfaces produced in situ. These observations permit a qualitative explanation of the difference in the electrical properties of junctions produced by these two techniques.

High temperature superconductor-normal metal-superconductor Josephson junctions with high characteristic voltages

We have fabricated step edge superconductor-normal metal-superconductor microbridges using YBa2Cu3O7−x(YBCO) and noble metals with critical current-normal resistance (IcRN) products as high as 10 mV and normal resistances up to 38 Ω. Our fabrication process achieves high values of the IcRN product by exploiting the anisotropy in the properties of epitaxial YBCO films, allowing contact only between normal metal and superconductor through the crystalline axes which support the largest Josephson coupling. This results in a dramatic increase in the normal resistance of a junction without decreasing its critical current. We discuss the role of the superconductor-normal metal boundary resistance on the junction electrical properties. We have coupled submillimeter wave rf currents quasioptically into junctions integrated at the feeds of noble metal planar log periodic antennas and have induced up to 7 Shapiro steps in the current-voltage characteristics with a 760 GHz beam from a far infrared laser.

Schottky barrier measurement by electron energy loss spectroscopy

It is difficult to imagine an electrical property which is more crucial to the success of modern device structures than the Schottky Barrier. In spite of this, the mechanism of barrier formation is still imperfectly understood, because the barrier formation is essentially a result of the details of the micro-structure of the metal/semiconductor interface. High resolution microscopy can obtain the microstructure of small regions of interfaces, but typical tools for measuring electronic structure have been able to measure only the bulk, or average, properties. Recently, scanning tunneling microscopy, using ballistically injected electrons, was used to obtain I-V characteristic of a buried junction. It was possible to image the junction in the plan-view geometry to show how the junction electrical properties change on a scale of 1 nm. These studies showed barrier changes with morphology and promise to provide useful insight into the problem. However, the studies do not obtain electrical properties as a function of distance away from the junction. This information is needed to help understand the underlying physics of the barrier formation. Thus, there is a need for an analytical tool which is compatible with the high resolution TEM imaging of interfaces in the cross-section geometry. Electron energy loss scattering can provide this tool if a small probe and a high energy resolution can be obtained.

Electrical Properties of Junctions between Sputter Deposited Silicon Films and Monocrystalline Silicon

physica status solidi (a)Volume 79, Issue 1 p. K21-K24 Short Note Electrical Properties of Junctions between Sputter Deposited Silicon Films and Monocrystalline Silicon J. Koshy, J. Koshy Department of Physics, Federal University of Technology, Bauchi Search for more papers by this author J. Koshy, J. Koshy Department of Physics, Federal University of Technology, Bauchi Search for more papers by this author First published: 16 September 1983 https://doi.org/10.1002/pssa.2210790144Citations: 2 PMB 02 48, Bauchi, Nigeria. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume79, Issue116 September 1983Pages K21-K24 RelatedInformation

Tunneling current density j(V) for Pb–In–Au alloy junctions and tunnel barrier modeling

Tunnel barriers formed by rf oxidation of Pb–In–Au alloys and consisting largely of In2O3 have been studied by measuring the current density as a function of applied voltage j(V) for voltages up to 1 V. The junctions studied here, which were oxidized on Pb- or photoresist-coated rf cathodes, showed no evidence of a barrier height below about 1 eV. A trapezoidal barrier with a height of at least 1 eV and a thickness equal to that of the oxide film, roughly 6 nm, would have a tunneling current far below that observed for these junctions. Furthermore, the measured j(V) curves were inconsistent with those calculated for a trapezoidal barrier, even for a barrier thickness less than the physical oxide thickness. The j(V) curves were, however, similar to those calculated for tunneling through a Schottky barrier in the indium oxide at the interface with the counterelectrode. Such a barrier, which is also suggested by recent measurements of oxide thickness and junction electrical properties at low voltages, might be expected to form between the metal electrodes and In2O3, which can be a degenerately-doped n-type semiconductor.

Characterization of Nb/Nb oxide structures in Josephson tunnel junctions

The subgap conductance of Nb, Nb oxide/Pb-alloy Josephson tunnel junctions was found to strongly depend on the rf plasma processing used to form the Nb oxide tunnel barrier. We have therefore studied the Nb/Nb oxide structures after rf plasma processing using x-ray photoelectron spectroscopy (XPS) and transmission electron microscropy (TEM) data. A crystalline Nb-C-O layer was formed as a transition region between the polycrystalline Nb base electrode and the Nb 2 O 5 tunnel barrier. The thickness of this transition region is sensitive to the rf plasma cleaning conditions prior to the tunnel barrier formation. An unexpected relation between junction electrical properties and the Nb/Nb oxide structure exists. The lowest subgap conductances are those obtained for tunnel junctions with transition regions about 30A thick. An abrupt interface between Nb and Nb 2 O 5 leads to junctions with high subgap conductances.

Electrical properties of junctions between Ge films and monocrystalline silicon

Junctions were fabricated by rf sputter deposition of germanium films onto chemically etched p-and n-type silicon crystals. The electrical properties are studied by I–U and C–U measurements. Heat-treated (400 °C) junctions show particularly reproducible properties and for these the barrier height to p-Si is 0.8 eV while that to n-Si is 0.3 eV. This offers technological applications by giving blocking contacts to p-Si and ohmic to n-Si. Unannealed junctions show somewhat higher hole barrier and also higher electron barrier, revealing the existence of radiation damage after the sputter deposition. At low frequencies the C–U measurements show excess capacitance, compared with what is expected for an abrupt junction. This indicates the contribution of states in the Ge film and at the interface. Durch HF-Aufspruhverfahren von Germaniumschichten auf chemisch geatzte p- und n-leitende Si-Kristalle werden Ubergange hergestellt. Die elektrischen Eigenschaften werden mit I–U- und C–U-Messungen untersucht. Warmebehandelte (400 °C) Ubergange zeigen besonders reproduzierbare Eigenschaften und die Barrierenhohe zu p-Si betragt 0,8 eV wahrend sie zu n-Si 0,3 eV betragt. Dies ergibt technologische Anwendugsmoglichkeiten fur sperrende Kontakte mit p-Si und ohmsche mit n-Si. Ungetemperte Ubergange zeigen etwas hohere Locherbarrieren und eben falls hohere Elektronenbarrieren, die auf die Existenz von Strahlungsdamage nach dem Spruhauftrag hinweisen. Bei niedrigen Frequenzen zeigen die C–U-Messungen zusatzliche Kapazitat im Vergleich zu der, die fur einen abrupten Ubergang erwartet wird. Dies ergibt einen Hinweis auf den Beitrag von Zustanden in der Ge-Schicht und an der Grenzflache.

Preparation of GaAs-Ge and InAs-GaAs Heterojunctions in a Closed Tube System Using Iodine Process

Preparation of single crystal heterojuctions is investigated in the vapor growth of GaAs on Ge or of InAs on GaAs substrate by varying their basic growth parameters such as source and substrate temperatures, iodine carrier concentration and crystal orientation. The relations between growth conditions, growth rate and crystal quality are discussed. The most remarkable feature is the appearance of an intermediate layer of 10–20 µ thick between substrate and grown film which is observed over a rather wide range of growth conditions and which plays a fairly important role in junction electrical properties. Experimental results suggested that the origin of this intermediate layer was strongly connected with the species that was once vaporized from the substrate and precipitated in the closed tube.