Showing papers on "Schottky barrier published in 1994"

Ferroelectric Schottky diode.

Abstract: A Schottky contact consisting of a semiconducting ferroelectric material and a high work function metal shows a bistable conduction characteristic. An on/off ratio of about 2 orders of magnitude was obtained in a structure consisting of a 0.2 \ensuremath{\mu}m ferroelectric PbTi${\mathrm{O}}_{3}$ film, a Au Schottky contact, and a ${\mathrm{La}}_{0.5}$${\mathrm{Sr}}_{0.5}$Co${\mathrm{O}}_{3}$ Ohmic bottom electrode. The observations are explained by a model in which the depletion width of the ferroelectric Schottky diode is determined by the polarization dependence of the internal electric field at the metal-ferroelectric interface.

Photoconductivity of Ultrathin Zinc Oxide Films

Abstract: Electrical and photoelectrical properties of nondoped and doped zinc oxide films coated on glass plates by the dip-coating method are investigated at room temperature in various ambient atmospheres. The dark conductivity of the nondoped films exponentially decreased with decreasing film thickness while the conductivity under illumination of 350 nm light was almost constant at 100 Scm-1 irrespective of the film thickness. Consequently thinner films showed larger photoresponse than thicker films. This thickness dependence is explained by the variation of ZnO particle size with the film thickness (fine particle model) and the additional effect of the Schottky barrier generated between the film and gold electrodes.

Switching element with memory provided with Schottky tunnelling barrier

Abstract: A switching element is provided with two electrodes (1, 2) with a semiconducting dielectric (3) therebetween, one electrode (2) having a material which forms a Schottky contact with the semiconducting dielectric (3), while a space charge region (3') of the Schottky contact forms a tunnelling barrier for electrons during operation. It is desirable in many applications for the switching element to hold a certain switching state, such as open or closed, during a longer period. The switching element may then be used, for example, as a memory element. The dielectric (3) includes a ferroelectric material with a remanent polarization which influences a dimension of the tunnelling barrier. In this manner the switching element has various switching states depending on the remanent polarization of the dielectric (3). These switching states are held until the polarization of the dielectric (3) changes.

Schottky barrier rectifier with mos trench

Abstract: A trench MOS Schottky barrier rectifier includes a semiconductor substrate having first and second faces, a cathode region of first conductivity type at the first face and a drift region of first conductivity type on the cathode region, extending to the second face. First and second trenches are formed in the drift region at the second face and define a mesa of first conductivity type therebetween. The mesa can be rectangular or circular in shape or of stripe geometry. Insulating regions are defined on the sidewalls of the trenches, adjacent the mesa, and an anode electrode is formed on the insulating regions, and on the top of the mesa at the second face. The anode electrode forms a Schottky rectifying contact with the mesa. The magnitude of reverse-biased leakage currents in the mesa and the susceptibility to reverse breakdown are limited not only by the potential barrier formed by the rectifying contact but also by the potential difference between the mesa and the portion of anode electrode extending along the insulating regions.Moreover, by properly choosing the width of the mesa, and by doping the mesa to a concentration greater than about 1x1016 per cubic centimeters, reverse blocking voltages greater than those of a corresponding parallel-plane P-N junction rectifier can be achieved.

Influence of barrier height distribution on the parameters of schottky diodes

Abstract: I‐V curves of Schottky diodes are simulated for a Gaussian type of the Schottky barrier height (SBH) distribution using the model of noninteracting parallel diodes. The mean value and the standard deviation of the distribution are supposed to be constant, i.e., not dependent on the voltage and the temperature. The influence of the distribution parameters and the temperature on the apparent barrier height and the ideality factor is analyzed. It is shown that the ideality factor increases and the apparent barrier height decreases with increasing standard deviation and decreasing temperature. The simulation also provides a rough estimate for the standard deviation. Values of ∼0.09 V can result in ideality factors up to 1.2. The importance of the effect of series resistance in the approach of noninteracting diodes is emphasized.

Schottky diodes with high series resistance: Limitations of forward I‐V methods

Abstract: Some methods have been proposed to deduce the value of Schottky parameters from forward I‐V characteristic even in the presence of a large series resistance. In this paper, some well‐known methods have been applied to experimental data of a real diode and to computer calculated curves. A comparison is made between these methods and the standard procedure. Some indications are given on the validity and the main limitations of all these techniques.

Silicon field-effect transistor based on quantum tunneling

Abstract: This letter explores regulation of current flow within a silicon field‐effect transistor by gate‐induced tunneling through a Schottky barrier located at the interface between a metallic source electrode and the Si channel. The goal here is to forestall short‐channel effects which are expected to prevent further size reductions in conventional devices when linewidths reach ∼1000 A. Control of tunneling appears to be possible at minimum channel lengths L∼250 A or less while simultaneously eliminating the need for large‐area source and drain contacts, so that scaling of Si transistors could be significantly extended if this principle proves technically feasible.

Influence of defect passivation by hydrogen on the Schottky barrier height of GaAs and InP contacts

Abstract: The change in barrier height caused by sputter metallization of contacts on both GaAs and InP substrates, and using evaporated contacts as a reference, is investigated. It has been found that by annealing, the reference barrier height can be restored. A model is proposed, wherein sputter metallization leads to passivation of interfacial defects by hydrogen. Accordingly, the Fermi level pinning caused by these defects is removed and the barrier height changes and is determined by other mechanisms. Annealing produces a removal of hydrogen and reactivates the amphoteric defects. Additional evidence is given for the assumption that sputter metallization leads to passivation, by hydrogen, of dopants and defects in the semiconductor.

Non‐ohmic characteristics of ZnO‐V2O5 ceramics

Abstract: The densification behavior, microstructure, and electrical properties of ZnO‐V2O5 ceramics were studied with V2O5 as the only additive ranging from 0.01 to 1.0 mol %. The addition of V2O5 to zinc oxide shows a tendency to enhance the densification rate and promote grain growth. However, a microstructure that consisted of anomalously grown grains was found for the specimens containing V2O5≥0.05 mol % when sintered at 1100 °C for 2 h. The x‐ray diffraction and SEM‐EDS microanalysis revealed that the sintered specimens had a two‐phase microstructure, i.e., a vanadium‐rich intergranular phase formed between ZnO grains. The formation of the grain boundary barrier layer was confirmed by the non‐ohmic I‐V behavior and the quick drop of apparent dielectric constant with increasing frequency of the ceramics. A nonlinearity coefficient of 2.4–2.8 was obtained at a current density of 10 mA/cm2 for a series ZnO‐V2O5 ceramics, and a Schottky barrier height of 0.44–0.47 eV (at 25 °C) was determined from the I‐V and C‐V experimental data, based on the thermionic emission theory, and the model of back‐to‐back double Schottky barriers.

Delta-doped Schottky diode nonlinear transmission lines for 480-fs, 3.5-V transients

Abstract: Waveforms having 480‐fs, 3.5‐V transients were generated with a delta‐doped GaAs Schottky diode nonlinear transmission line and measured with an on‐chip diode sampling bridge at room temperature. Integration of delta‐doped diodes with high C(V) nonlinearity and uniform‐doped diodes with high speed made possible a transient waveform two times shorter than any previously measured.

Electrical characterisation of Ti Schottky barriers on n-type GaN

Abstract: The Schottky barrier height of Ti on n-type GaN has been measured to be 0.58 and 0.59 eV by capacitance-voltage and current-voltage techniques, respectively. This work is of particular interest because it is the first measure of the Schottky barrier height on GaN for a metal other than Au. The barrier height of Ti on GaN is significantly less than that of Au. This supports the prediction that the Fermi level is not pinned at the GaN surface.

Influence of interfacial hydrogen and oxygen on the Schottky barrier height of nickel on (111) and (100) diamond surfaces.

Abstract: In this paper we report on Schottky barrier height measurements of nickel on both diamond (111) and (100) surfaces, as a function of surface preparation. The Schottky barriers of thin (5 \AA{}) nickel films on natural type-IIb (p-type semiconducting) diamond (111) and (100) surfaces were determined with ultraviolet photoemission spectroscopy. Exposing the diamond (111) surfaces to an argon plasma while heated to 350 \ifmmode^\circ\else\textdegree\fi{}C resulted in a change from a negative-electron-affinity surface to a positive-electron-affinity surface. This effect was used as an indication that a hydrogen-free surface had been obtained. Deposition of a monolayer of nickel on the hydrogen-free diamond (111) surface resulted in a Schottky barrier height of 0.5 eV. The nickel caused the surface to exhibit a negative-electron-affinity surface. Nickel deposited on a diamond (111) surface with a negative electron affinity, indicative of a monohydride-terminated surface, resulted in a \ensuremath{\sim}1.0-eV Schottky barrier height. Diamond (100) surfaces were prepared by vacuum annealing to temperatures ranging from 500 \ifmmode^\circ\else\textdegree\fi{}C to 1070 \ifmmode^\circ\else\textdegree\fi{}C. The various anneals resulted in a lowering of the electron affinity by up to \ensuremath{\sim}1 eV, which resulted in a negative electron affinity after the surface had been annealed to \ensuremath{\sim}1000 \ifmmode^\circ\else\textdegree\fi{}C. Oxygen was initially present on the surface but could not be observed after the 1000 \ifmmode^\circ\else\textdegree\fi{}C anneal. The removal of oxygen and the appearance of a negative electron affinity coincided with the appearance of a 2\ifmmode\times\else\texttimes\fi{}1 surface reconstruction. Nickel was deposited after the various anneals, and Schottky barrier heights were found, ranging from 1.5 eV for the 545 \ifmmode^\circ\else\textdegree\fi{}C-annealed surface to 0.7 eV for the 1070 \ifmmode^\circ\else\textdegree\fi{}C-annealed surface. These measurements suggest that for both the (111) and the (100) diamond surfaces the presence of chemisorbed species, such as hydrogen and oxygen, results in an increase in the Schottky barrier height.

A simple edge termination for silicon carbide devices with nearly ideal breakdown voltage

Abstract: In this paper, a simple edge termination is described which can achieve near ideal parallel plane breakdown for silicon carbide devices. This novel edge termination involves self aligned implantation of a neutral species on the edges of devices to form an amorphous layer. With this termination formed using argon implantation, the breakdown voltage of Schottky barrier diodes was measured to be very close to ideal plane parallel breakdown voltage. >

Evidence for field enhanced electron capture by EL2 centers in semi‐insulating GaAs and the effect on GaAs radiation detectors

Abstract: The performance of Schottky contact semiconductor radiation detectors fabricated from semi‐insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi‐insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi‐insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements.

140-GHz metal-semiconductor-metal photodetectors on silicon-on-insulator substrate with a scaled active layer

Abstract: Metal‐semiconductor‐metal photodetectors with 100‐nm finger spacing and width on a silicon‐on‐insulator substrate that has a scaled active layer were fabricated and characterized using electro‐optic sampling. The unique device structure cuts off carriers generated deep inside the semiconductor substrate, resulting in a measured response time of 3.2 ps and a bandwidth of 140 GHz. Furthermore, the detector structure makes the detector’s speed independent of the light penetration depth and thus the light wavelength. Good metal‐semiconductor Schottky contact and low detector dark current have been achieved.

Schottky barrier height of metal contacts to p‐type alpha 6H‐SiC

Abstract: A survey of metal (Pd, Ni, Au, Ag, Mg, Ti, and Al) Schottky barrier contact formation to p‐type Si‐face (0001) and C‐face (0001) 6H‐SiC by using x‐ray photoemission spectroscopy is reported. The Schottky barrier height φB ranges from 1.17 to 2.56 eV and is influenced by the contact metal work function and the 6H‐SiC crystal face. A comparison with prior φB values for n‐type material indicates that for similarly prepared metal/6H‐SiC interfaces (including those which have been annealed) φBp and φBn sum to the 6H‐SiC band gap.

Barrier Heights of Metal Contacts on H-Terminated Diamond: Explanation by Metal-Induced Gap States and Interface Dipoles

Abstract: Barrier heights reported by Kawarada et al. for metal contacts on H-terminated p-diamond surfaces are by approximately 1 eV smaller than what was found earlier with the same metals on clean p-diamond surfaces. The latter data are explained by the model that the continuum of metal-induced gap states determines the barrier heights in metal-semiconductor contacts and the charge transfer across such interfaces may be described by the difference of the metal and semiconductor electronegatives. Both sign and magnitude of the H-induced lowering of the barrier heights on p-diamond are explained by an interface layer of additional H–C dipoles.

Electric Properties of Metal/Diamond Interfaces Utilizing Hydrogen-Terminated Surfaces of Homoepitaxial Diamonds

Abstract: As-grown homoepitaxial diamond surfaces fabricated by chemical vapor deposition are terminated by hydrogen, and are expected to have a low density of surface states. On such diamond surfaces, high-quality Schottky contacts have been obtained utilizing metals with low electronegativities, such as Al or Pb. The ideality factors of those point contacts to diamond are less than 1.1, which is the nearest value to unity ever reported in diamonds. Quantitative measurements of Schottky barrier heights at various metal contacts have also been performed. A strong correlation between the barrier heights and the metal electronegativities is observed. Even an ohmic property is obtained when metals with higher electronegativities were used. The effect of Fermi level pinning is reduced at the interfaces between metals and hydrogen-terminated diamonds.

Numerical Simulation of Tunnel Effect Transistors Employing Internal Field Emission of Schottky Barrier Junction

Abstract: Tunnel transistors employing internal field emission of the Schottky barrier junction (SBTT) are expected to be a promising component for high-density and low-cost integrated circuits. In order to characterize the performance of SBTT, we carried out 2-D numerical simulation on four typical device structures. The output characteristics of SBTT are basically triodelike; that is, the drain current increases exponentially with increasing gate voltage, having high and nonlinear transfer performance, as elucidated by the simulation. This triodelike characteristic is observed when the channel layer is thicker than the depletion layer width formed by gate bias near the drain. In the case of a thin channel layer, a saturation feature of the drain current with increasing gate bias appears due to a pinch-off effect, which is favorable for reducing the leakage current in the off state. A prototype n-channel SBTT of crystalline silicon was fabricated and its transistor action was confirmed.

Metal-insulator-semiconductor Schottky-type diodes of doped thiophene oligomers

Abstract: Schottky barrier diodes were made from films of the thiophene oligomer α,α′-coupled dodecathiophene substituted with four n-dodecyl side chains, T12d4(2,5,8,11), which were doped in solution with various amounts of mainly 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Eutectic GaIn alloy or evaporated In were applied as Schottky contacts. The diodes exhibited strong rectification up to 106 at +1 V/−1 V, diode quality factors between 1.2 and 2, and forward current densities up to a few A cm−2 at 1 V forward bias. Analysis of complex impedance spectra and capacitance-voltage measurements showed that the impedance of the diodes is due to the actual Schottky junction, which is similar for all doped diodes, and to a ‘non-conducting’ interface layer which is formed by chemical reaction upon application of the Schottky metal. Current transport at high forward bias is not bulk limited, but due to charge injection across this thin interfacial film and, hence, manifested as space charge limited current. It will be argued that the diodes can tentatively be described as metal-insulator-semiconductor (MIS) Schottky diodes with a graded dopant profile. This interpretation is also supported by a correlation found between forward and saturation current densities.

Schottky effect at a metal‐polymer interface

Abstract: We report the observation of the Schottky effect at the interface between a metal and a semiconducting polymer by means of internal photoemission spectroscopy. The bias dependence of the barrier provides information on the electrical properties of the polymer.

Video detection and mixing performance of GaAs Schottky‐barrier diodes at 30 THz and comparison with metal‐insulator‐metal diodes

Abstract: Video detection experiments from 0.7 to 30 THz and mixing experiments at 30 THz have been performed with GaAs Schottky‐barrier diodes and W‐Ni metal‐insulator‐metal (MIM) diodes. Above approximately 12 THz the MIM diode is the more sensitive video detector (a factor of 5–10 at 30 THz). Difference frequencies up to 34 GHz were generated by mixing the radiation of two adjacent CO2 laser lines and a microwave source in a Schottky‐barrier diode. The dependence of the mixing signal on different diode parameters (doping density, plasma frequency, cutoff frequency) and on bias current was measured. Compared with MIM diodes at 30 THz the Schottky‐barrier diodes are less efficient for mixing (a factor of 104). The results suggest that thermionic emission is the dominant physical mechanism responsible for video detection and mixing at 30 THz.

Design of ohmic contacts to p‐ZnSe

Abstract: First‐principle density functional calculations are used to design improved ohmic contacts to p‐ZnSe. Two design strategies are applied: the use of a graded semiconductor epilayer with a large valence band offset, and the imposition of an interlayer to reduce the metal/p‐ZnSe Schottky barrier. In the former strategy we study BeTe because it is lattice matched to ZnSe. We find the BeTe/ZnSe valence band offset is nearly the same as the ZnTe/ZnSe offset, so that if BeTe can be sufficiently p doped, its grading with ZnSe should lead to an ohmic contact comparable to a ZnTe‐grading contact, but without the deleterious presence of misfit dislocations. For the latter strategy we consider the use of a thin As‐Si interlayer between the II‐VI material and metal. The As effects an extra microscopic dipole at the interface that lowers the Fermi level 1 eV in the II‐VI band gap, leading to greatly decreased rectification at p‐type contacts. Applying both strategies simultaneously suggests that a metal/Si‐As/BeTe/ZnSe multilayer structure would afford a nearly ideal ohmic contact to p‐ZnSe.

A direct and accurate method for the extraction of diffusion length and surface recombination velocity from an EBIC line scan

Abstract: A new method is proposed for the determination of bulk minority carrier diffusion length and surface recombination velocity. This method uses data from an EBIC line scan in which the current collecting p − n junction or Schottky barrier is parallel to the electron beam. A 3-D computer simulation was used to verify the accuracy of the method. It was found that this method is simpler to use and more accurate than existing methods.

Nanometer-resolved spatial variations in the Schottky barrier height of a Au/n-type GaAs diode.

Abstract: Nanometer-resolved lateral variations in the Schottky barrier height (SBH) formed at a chemically prepared Au/n-type GaAs interface were measured using ballistic-electron-emission microscopy (BEEM). The spatial profile and the statistical distribution of the SBH's thus obtained were compared to current-voltage (IV) and capacitance-voltage (CV) characteristics of the same metal-semiconductor contact. This comparison showed that the macroscopic SBH obtained from the IV measurements can be successfully interpreted using the parallel conduction model applied to the BEEM-derived distribution, if the effect of thermionic field emission is included. The SBH obtained from the CV measurements is greater than the mean value obtained from BEEM measurements by nearly the image-force lowering expected for a Au/GaAs diode.

Schottky barrier MOSFET systems and fabrication thereof

Abstract: (MOS) device systems-utilizing Schottky barrier source and drain to channel region junctions are disclosed. Experimentally derived results which demonstrate operation of fabricated N-channel and P-channel Schottky barrier (MOSFET) devices, and of fabricated single devices with operational characteristics similar to (CMOS) and to a non-latching (SRC) are reported. Use of essentially non-rectifying Schottky barriers in (MOS) structures involving highly doped and the like and intrinsic semiconductor to allow non-rectifying interconnection of, and electrical accessing of device regions is also disclosed. Insulator effected low leakage current device geometries and fabrication procedures therefore are taught. Selective electrical interconnection of drain to drain, source to drain, or source to source, of N-channel and/or P-channel Schottky barrier (MOSFET) devices formed on P-type, N-type and Intrinsic semiconductor allows realization of Schottky Barrier (CMOS), (MOSFET) with (MOSFET) load, balanced differential (MOSFET) device systems and inverting and non-inverting single devices with operating characteristics similar to (CMOS), which devices can be utilized in modulation, as well as in voltage controled switching and effecting a direction of rectification.

The effect of alpha-particle and proton irradiation on the electrical and defect properties of n-GaAs

Abstract: Radiation damage effects were studied in n-GaAs grown by organo-metallic vapour phase epitaxy (OMVPE) for a wide range of alpha-particle (2.0 MeV and 5.4 MeV) and proton (2.0 MeV) particle fluences, using an americium-241 (Am-241) radio-nuclide and a linear Van de Graaff accelerator as the particle sources. The samples were irradiated at 300 K, after fabricating palladium Schottky barrier diodes (SBDs) on the 1.2 × 1016 cm3 Si-doped epitaxial layers. The irradiation-induced defects are characterized using conventional deep level transient spectroscopy (DLTS). A correlation is made between the change in SBD characteristics and the quantity and type of defects introduced during irradiation. It is shown that the two parameters most susceptible to this irradiation are the reverse leakage current of the SBDs and the free carrier density of the epilayer. The introduction rate and the “signatures” of the alpha-particle and proton irradiation-induced defects are calculated and compared to those of similar defects introduced during electron irradiation.