Showing papers on "Schottky barrier published in 1977"

Photoelectrolysis and physical properties of the semiconducting electrode WO2

Abstract: The behavior of semiconducting electrodes for photoelectrolysis of water is examined in terms of the physical properties of the semiconductor. The semiconductor‐electrolyte junction is treated as a simple Schottky barrier, and the photocurrent is described using this model. The approach is appropriate since large‐band‐gap semiconductors have an intrinsic oxygen overpotential which removes the electrode reaction kinetics as the rate‐limiting step. The model is successful in describing the wavelength and potential dependence of the photocurrent in WO3 and allows a determination of the band gap, optical absorption depth, minority‐carrier diffusion length, flat‐band potential, and the nature of the fundamental optical transition (direct or indirect). It is shown for WO3 that minority‐carrier diffusion plays a limited role in determining the photoresponse of the semiconductor‐electrolyte junction. There are indications that the diffusion length in this low carrier mobility material is determined by diffusion‐controlled bulk recombination processes rather than the more common trap‐limited recombination. It is also shown that the fundamental optical transition is indirect and that the band‐gap energy depends relatively strongly on applied potential and electrolyte. This effect seems to be the result of field‐induced crystallographic distortions in antiferroelectric WO3.

Ionicity and the theory of Schottky barriers

Abstract: We have investigated the role of ionicity in metal-semiconductor Schottky barriers by examining interfaces of increasing semiconductor ionicity. The electronic structure of four separate interfaces consisting of jellium (of Al density) in contact with the (111) surface of Si and the (110) surfaces of GaAs, ZnSe, and ZnS is investigated through the use of a self-consistent pseudopotential method. The barrier height and the surface density of states in the semiconductor band gap are determined. The phenomenological index of interface behavior S (studied by Kurtin, McGill, and Mead for semiconductors of different ionicity) is discussed in terms of a simple model involving metal-induced states in the semiconductor gap.

Theory of metal‐insulator‐semiconductor solar cells

Abstract: Recent reports in the literature indicate that the introduction of an interfacial oxide layer in a Schottky barrier can greatly increase the photovoltaic conversion efficiency of such devices. We propose an explanation for the operation of such solar cells based on the concept that they are minority‐carrier nonequilibrium MIS tunnel diodes. Calculations of efficiency as a function of insulator thickness, substrate carrier concentration, surfaces states, and oxide charge are presented. These indicate that a maximum theoretical efficiency of 21% is possible under AM2 illumination for high substrate doping and low interface defect density.

Method for fabricating tantalum semiconductor contacts

Abstract: A silicon semiconductor device having contacts which include tantalum. The tantalum is useful in particular for fabricating Schottky barrier diodes having a low barrier height. The method includes: precleaning the silicon substrate prior to depositing the tantalum; depositing the tantalum at low pressure and low substrate temperature to avoid oxidation of the tantalum; and sintering the contact to reduce any interfacial charges and films remaining between the silicon and tantalum. When a metal which reacts with silicon during processing, such as aluminum, is used as interconnection metallurgy, a layer of chrome must be deposited between the tantalum and aluminum.

Solar cells using discharge-produced amorphous silicon

Abstract: Thin film solar cells, ≲ 1 μm thick, have been fabricated in p-i-n and Schottky barrier structures using d.c. and r.f. glow discharges in silane. Conversion efficiencies in the range of 2.5 to 4.0% have been obtained with both structures. The p-i-n cells exhibit built-in potentials of ∼ 1.1 V while the Pt Schottky barrier cells have barrier heights of ∼ 1.1 eV. The dark currents in the p-i-n cells appear to be recombination-limited while the Schottky barrier cells exhibit near-ideal diode characteristics with diode quality factors near unity.

Entrance Windows in Germanium Low-Energy X-Ray Detectors

Abstract: We have found experimentally that high-purity Ge low-energy X-ray detectors have a relatively thick entrance window which renders them practically useless below ~ 2.3 KeV. A simple X-ray fluorescence experiment establishes clearly that the window is physically in the Ge material itself. Experiments with detectors made from different Ge crystals, and with Schottky barrier contacts of different metals indicate that the effect is due to a basic property of the transport of electrons near a surface. Theoretical considerations and a Monte Carlo calculation show that the window is caused by the escape of warm electrons which are the end product of a photo event. The mean free path of the electrons becomes longer as they lose energy by optical phonon collisions and they can be trapped at the surface before they are picked up by the electric field.

Theoretical analysis of the quantum photoelectric yield in schottky diodes

Abstract: A detailed analytical calculation of the photoelectric quantum yield in Schottky diodes is presented. The transport of carriers in the surface space charge region is treated explicitly, taking account of photogeneration, diffusion and drift in the non-uniform electric field. Boundary conditions at the interface are expressed in terms of surface recombination velocity and emission velocity of excess carriers into the metal. It is shown that the metal-semiconductor interface strongly affects the collection efficiency of short wavelength generated electron-hole pairs. This effect basically originates in the emission flux of majority carriers into the metal. Current, charge carriers distributions and quantum yields are computed using the data of AuCdTe Schottky barriers.

Preparation and Properties of InS Single Crystals

Abstract: We report the preparation and properties of single crystals of the III-VI compound semiconductor InS. Using the solution-growth method from In melt we have prepared single crystals of InS large enough to perform some electrical and optical measurements. The electrical measurements reveal that resistivity parallel to the c-axis of InS is 10~100 times larger than that perpendicular to the axis. Also, the carrier concentration of as-grown crystals indicating always n-type conduction is more than 1018 cm-3 and the Hall mobility is about 50 cm2/V sec at room temperature. The experimental data of optical absorption, electroreflectance and photoresponse at the Au-InS Schottky barrier show that the indirect band gap is at 1.90 eV and the direct gap at 2.44 eV at room temperature. The electroreflectance data also reveal structure associated with some higher interband critical points in the energy region from 2.5 to 4.0 eV.

Dependence of the Si‐SiO2 barrier height on SiO2 thickness in MOS tunnel structures

Abstract: Ultrathin (10–30 A) SiO2 layers with large interface‐state densities were used as the dielectric between aluminum and degenerate silicon. The presence of interface states resulted in current‐vs‐voltage curves characteristic of metal‐insulator‐metal (MIM) tunnel structures. MIM tunneling theory was used to estimate the Si‐SiO2 (φSi‐SiO2) and the Al‐SiO2 (φAl‐SiO2) barrier heights. We found that the Si‐SiO2 barrier height increased from 0.42 eV at 10 A to 0.65 eV for 25.5 A of SiO2 on degenerate p‐type Si, and from 0.64 eV at 14 A to 1.27 eV for 29.3 A of SiO2 on degenerate n‐type Si. The Al‐SiO2 barrier height could not be consistently determined but was about 0.61±0.16 eV. A smooth transition from Schottky barrier to MOS tunnel structure was observed. The thickness dependence of φSi‐SiO2 is most likely due to the recently observed 15–20‐A nonstoichiometric SiO transition region at the Si‐SiO2 interface.

Study of Al/Pd2Si contacts on Si

Abstract: An electrical and structural characterization of the Al/Pd2Si thin‐film system on n‐type Si was performed with the use of Schottky barrier contacts and subsequent heat‐treatment cycles Contact barrier energy φBn, as extracted from current–voltage and capacitance–voltage measurements, decreased initially from about 071 eV, characteristic of the Pd2Si interface, to a value of 065 eV Auger electron spectroscopy analysis indicates the observed decrease in φBn corresponds to the decomposition of the Pd2Si layer A drastic alteration of the diode morphology accompanied the decrease in φBn Successive heat treatments at higher temperatures and longer times produced little subsequent change in the structural form of the surface, but yielded an increase in φBn to a value greater than 081 eV Additional data indicated that Al may enter the n‐type Si as a compensating impurity during prolonged heat treatments

Low‐noise millimeter‐wave mixer diodes prepared by molecular beam epitaxy (MBE)

Abstract: Schottky barrier diodes which are specifically designed for use in cryogenically cooled millimeter‐wave mixers have been fabricated from MBE layers grown on heavily doped GaAs substrates. At 15 K the devices show a nearly exponential current‐voltage characteristic and a diode noise temperature which is determined predominantly by the tunneling transport mechanism. A diode noise temperature as low as 55 K was achieved under pumped conditions. This is the lowest diode noise temperature ever obtained in a resistive mixer. A single sideband mixer noise temperature of 315 K was measured at 102 GHz for a cryogenic mixer employing these diodes.

Efficiency calculations for thin-film polycrystalline semiconductor Schottky barrier solar cells

Abstract: Numerical calculations have been made of the effect of grain size on the short-circuit current and the AM1 efficiency of polycrystalline thin film InP, GaAs, and Si Schottky barrier solar cells. Si cells 10 µm thick are at best 8 percent efficient for 100-µm grain sizes; 25-µm-thick Si cells can be about 10 percent efficient for this grain size. GaAs cells 2 µm thick can be 12 percent efficient for grain sizes of 3 µm or greater.

Model calculations for metal-insulator-semiconductor solar cells

Abstract: An analytical approach to calculating MIS solar cell properties has been formulated and utilized to study solar cell efficiency as a function of interfacial layer thickness, various interfacial film parameters and band gap. Three models are considered regarding interface state recombination kinetics. Calculations are presented for the case of interface states being in equilibrium with the metal (Model (I), in equilibrium with the majority carriers of the semiconductor (Model II) and in equilibrium with the minority carriers (Model III). It is found that in all three cases, the efficiency of low barrier height, Schottky barrier cells can be increased very significantly. For example, it is shown that for a band gap of 1.5 eV and a barrier height of 0.5 eV, it appears possible to increase the cell efficiency from essentially zero to 12%. If the barrier height is 1.0 eV, an efficiency of over 20% is possible. It is determined, however, that MIS solar cell performance is limited by leakage currents due to minority carrier diffusion back into the bulk. As a result, the upper limit of performance is defined by that for a homojunction. These calculations identify ranges of surface state density and interfacial barrier heights necessary for a good MIS solar cell.

High voltage Schottky barrier diode

Abstract: An improved high voltage Schottky barrier diode includes a semiconductor layer having two adjacent sublayers of the same type conductivity but different doping concentrations. A plurality of isolated discrete regions of a second type conductivity opposite to that of the first are provided along the boundary region between the sublayers and beneath the Schottky junction. The invention results in an improved high voltage Schottky diode in which the reverse characteristics are substantially enhanced.

High temperature annealing behaviour of Schottky barriers on GaAs with gold and gold-gallium contacts

Abstract: It is shown that unlike AuGaAs Schottky diodes, a Schottky barrier made on GaAs using an evaporated film of AuGa eutectic alloy does not degrade on heat treatment. It is shown that the presence of Ga in the top contact prevents micro-alloying to take place during heat treatment and thus prevents degradation of the diode behaviour.

Composition‐tuned PbSxSe1−x Schottky‐barrier infrared detectors

Abstract: Schottky‐barrier photodiodes were prepared by depositing either lead or indium onto p‐type PbSxSe1−x epitaxial films. These photodiodes had 77 °K zero‐bias resistance‐area products of 26–21 000 Ω cm2 as x varied from 0 to 1, respectively. The peak detectivities were close to the background limit and could be composition tuned between 3.7 and 6.9 μm at 77 °K. Narrowband detectors were prepared by using one film as a short‐wavelength cutoff filter and a second film, of slightly different composition, as the detector. These devices exhibit high quantum efficiencies, low half‐bandwidths, and insensitivity to variations in incident angle.

Conversion Loss Limitations on Schottky-Barrier Mixers (Short Papers)

Abstract: A new set of criteria involving diode area, material parameters, and temperature is introduced for the Schottky-barrier mixer diode that must be considered if its usage is to be extended to the submillimeter wavelength region or cryogenically cooled to reduce the noise contribution of the mixer. It has been well established that, in order to reduce the parasitic loss as the frequency is increased, it is necessary to reduce the area of the diode. What has not been analyzed heretofore is the effect that a reduction in diode area can have on the intrinsic conversion loss L/sub 0/ of the diode resulting from its nonlinear resistance. This analysis focuses on the competing requirements of impedance matching the diode to its imbedding circuit and the finite dynamic range of the nonlinear resistance. As a result, L/sub 0/ can increase rapidly as the area is reduced. Results are first expressed in terms of dimensionless parameters, and then some respresentative examples are investigated in detail. The following conclusions are drawn: a large Richardson constant extends the usefulness of the diode to smaller diameters, and hence, shorter wavelengths; cooling a thermionic emitting diode can have a very detrimental effect on L/sub 0/; impedance mismatching is found, in generaI, to be a necessity for minimum conversion loss; and large barrier heights are desirable for efficient tunnel emitter converters.

Interface state density in Au-nGaAs Schottky diodes

Abstract: A method for determining the surface state density in Schottky diodes taking into account both I–V and C–V data while considering the presence of a deep donor level is presented. The model assumes that the barrier height is controlled by the energy distribution of surface states in equilibrium with the metal and the applied potential and does not include, explicitly, an interfacial layer. The model was applied to extract interface state densities of Au- n GaAs guarded Schottky diodes fabricated from bulk and VPE (100) GaAs with carrier conentrations between 3 × 10 15 and 8 × 10 16 cm −3 . These diodes exhibited ideality ( n ) factors of approximately 1.02 and room temperature saturation current densities ∼10 −8 A/cm 2 . This model is in substantial agreement with forward bias measurements over the 77–360°K temperature range investigated, in that a temperature-independent energy distribution of interface states was obtained. In reverse bias the interface state model is most valid with the higher carrier concentration material and at high temperature and low bias voltage. Typical interface state densities from 0.07 eV above the zero bias Fermi level to 0.01 eV below the Fermi level were 2 × 10 13 cm −2 eV −1 . The validity of the model under reverse bias is restricted by a non-thermionic reverse current, thought to be enhance field emission from traps.

Photovoltaic device containing an organic layer

Abstract: A photovoltaic device for the conversion of light (preferably in the visible spectrum) to electrical current consists of at least two electrodes (one of which must be substantially transparent to the light), each electrode being made of different materials and in which one electrode comprises an element that has a work function (generally expressed in electron volts) greater than that of aluminum (e.g. gold or silver) and the other electrode comprises an element that has a work function equal to or less than that of aluminum (e.g., aluminum or magnesium). Sandwiched between and in contact with the electrodes is a photoresponsive organic layer comprising at least one organic compound which, in general, has the capacity to sensitize or de-sensitize silver halides, titanium dioxide, zinc oxide, cadmium sulfide, selenium and polyvinyl carbazole (examples of the organic compounds are the cyanine dyes, especially the merocyanine dyes). The electrode comprising an element having a work function equal to or less than aluminum forms a Schottky barrier with the organic layer. Optionally, an insulating film is interposed between the Schottky barrier elctrode and the organic layer.

Electrical characteristics of Au/Ti-(n-type) InP Schottky diodes

Abstract: Metal-semiconductor surface barriers have been formed by the vacuum evaporation of Au/Ti on to epitaxially grown films of n-type InP. The current and capacitance of these devices were measured as a function of voltage at several temperatures and analysed in terms of existing theories. The particular contact fabrication process which has been used produces a relatively high (0.53 eV) room-temperature barrier height; the temperature dependence of the barrier height (4.8*10-4 eV K-1) is approximately equal to that of the energy gap in InP. The diodes exhibited ideality factors of approximately 1.07 and room-temperature saturation current densities approximately 3*10-5 A cm-2.

Barrier height modification in silicon Schottky (MIS) solar cells

Abstract: A study of experimental data on Cr-oxide-p-Si solar cells has led to a metal evaporation procedure which gives 0.50 V oc oc . A high n-value and fixed charge in the oxide are not necessary to obtain a high V oc .

Submillimeter Heterodyne Detection with Planar GaAs Schottky-Barrier Diodes

Abstract: Planar surface-oriented Pt/GaAs Schottky-barrier diodes have been fabricated and used to detect signals at submillimeter wavelengths. Video detection has been observed up to frequencies as high as 890 GHz. Harmonic mixing between the ninth harmonic of a 74.21-GHz signal and the second harmonic of 333.95-GHz radiation has also been obtained.

Ion implanted Schottky barrier diode

Abstract: A Schottky barrier diode having a subsurface metalsemiconductor rectifying barrier with electrical rectification properties immune to semiconductor surface contamination. A special ion implantation technique is used to produce a very thin but strongly metallic island-like region in a semiconductive body. A Schottky barrier separates the region from the semiconductive body below the semiconductor body surface. A special truncated Gaussian profile in metal concentration through the thickness of the region provides low thermal and electrical resistance between the Schottky barrier and the region surface.

Barrier heights on cadmium telluride schottky solar cells

Abstract: Schottky barriers on N-type cadmium telluride have been studied in view of application to solar cells. The barrier heights, as determined by the photoresponse and forward current measurements show a linear dependence upon the metal work function. Barrier heights up to 0.90 eV have been reached for Pt-CdTe contacts. Open circuit voltages up to 680 mV have been measured for such cells. Investigation of the Au-CdTe barrier immediately after the deposition of the metal (no contact with air) has shown that the barrier is formed immediately under vacuum. However, when the device is brought in contact with air, the open circuit voltage increases due to an increase of the n factor.

Theory of the Schottky barrier solar cell

Abstract: A model of Schottky barrier solar cells with an interfacial layer is described which takes into account more accurately than has been done so far the dependence of barrier height on the interfacial density of states $(D\_{\text{S}})$ and consequently the various potential drops in the cell. This improvement tends to yield higher predicted efficiencies for low values of $D\_{\text{S}}$. Also taken into account is the recombination traffic through the interfacial states. This effect is important at high values of $D\_{\text{S}}$ when it lowers the predicted efficiency. Recombination in the transition and bulk regions is also considered, but this does not have a very marked effect. Numerical results are given for a Au-SiO$\_{2}$-Si contact. A new effect - the possible fanning out of the quasi-Fermi levels for the interfacial states - is also noted.

Measurement of minority carrier lifetime profiles in silicon

Abstract: The influence of finite surface recombination velocity on the measurement of minority carrier lifetime has been studied. The method is based on measuring the phase shift between the a.c.-photocurrent of a Schottky contact and the incident light. The limit of spatial resolution has been shown by theoretical calculations to be about one diffusion length. Lifetime profiles have been measured by the use of a mercury capillary contact.