Showing papers on "Schottky barrier published in 1985"

Schottky barriers and semiconductor band structures.

Abstract: Various models of Schottky-barrier formation suggest Fermi-level pinning in midgap. Elemen- tary band-structure considerations indicate that, for diamond-structure semiconductors, the physically relevant gap is the indirect gap, corrected for spin-orbit splitting. Schottky-barrier heights for elemental and III-V compound semiconductors can be predicted to 0.1 eV from measured indirect gaps and splittings. The dimensionless pinning strength S\ifmmode\bar\else\textasciimacron\fi{} is given by the optical dielectric constant. Chemical trends are thus simply explained.

Characterization of interface states at Ni/nCdF2 Schottky barrier type diodes and the effect of CdF2 surface preparation

Abstract: Two Schottky diodes were fabricated by evaporation of nickel on to an n-type CdF2:YF3 semiconductor. Diode A was prepared on a slightly etched polished surface and diode B on an unpolished strongly etched surface. The current-voltage (I-V), capacitance-voltage (C-V), and conductance-voltage (G-V) characteristics were determined at room temperature. Both diodes showed non-ideal I-V behaviour with ideality factors 1.5 and 2.0, respectively and are thought to have a metal-interface layer-semiconductor configuration. Under forward bias, the admittance showed large frequency dispersion possibly caused by the interface states in thermal equilibrium with the semiconductor. Analysis of the C-V data in terms of Lehovec's model of an interface state continuum required the supposition of two time constants differing by 2 to 3 orders of magnitude. The characteristic parameters of the interface states (energy position, density, time constant and capture cross-section) were obtained for the values of the forward bias in the range 0.0 V ≦ V ≦ 0.2 V. The diode B is found to have the interface state densities about two orders of magnitude higher than the diode A which may be attributed to the different surface treatments. The C-V measurements at 100 kHz also indicated the presence of a deep donor trap about 0.6 eV below the conduction band edge in diode A.

Study of forward I‐V plot for Schottky diodes with high series resistance

Abstract: The current‐voltage characteristics for Schottky barrier diodes with series resistance are discussed. It is shown that by using Norde’s function F(V)=V/2−(kT/q)ln(I/SAT2) at two different temperatures, barrier height, n‐value or ideality factor, and series resistance can be determined even in the case 1

The theory of hot-electron photoemission in Schottky-barrier IR detectors

Abstract: Two semiclassical ballistic transport models for thin films developed in 1971 treat the problem of "hot-electron" internal photoemission in Schottky-barrier diode IR detectors. Both formulations take into account multiple scattering from the surfaces as well as hot-electron-phonon and hot-electron-cold-electron collisions in the bulk. The models are compared for the case of uniform absorption and one of the models is then extended. The extensions incorporate the effect on internal quantum yield of small energy losses from electron-phonon collisions. Also, it is no longer assumed that the fraction removed by capture is small which insures that the yield cannot exceed the theoretical upper limit. The results are illustrated by Fowler plots over a range of scattering parameters and thicknesses germane to Schottky diodes of current interest, PtSi/Si and Pd 2 Si/Si. The main new features of the plots include curvature for photon energies close to the barrier energy due to phonon collision thermalization and roll-off at higher excitation energies whenever the yield is comparable in magnitude to the theoretical limit. The model is in good agreement with earlier Monte Carlo computations.

Correlation of Schottky-barrier height and microstructure in the epitaxial Ni silicide on Si(111)

Abstract: The correlation of Schottky-barrier height and microstructure has been investigated with three types of epitaxial Ni silicides, type-$A$ and -$B$ Ni${\mathrm{Si}}_{2}$ and NiSi, on Si(111) substrates. All these interfaces can be formed to yield a barrier height of 0.78 eV. This high barrier was obtained only for near-perfect interfaces; otherwise-less-perfect silicides yielded low barrier heights of 0.66 eV. This barrier height is controlled primarily by the structural perfection of the interface rather than by the specific type of epitaxy.

Field drift of the hydrogen‐related, acceptor‐neutralizing defect in diodes from hydrogenated silicon

Abstract: Field drift of the hydrogen‐related, acceptor‐neutralizing defect has been detected in reverse‐biased Schottky barrier and junction diodes made from plasma‐hydrogenated, p‐type, boron‐doped silicon. Significant differences in diffusion depths and drift rates between hydrogenated and deuterated silicon indicate that the mobile neutralizing species is possibly uncomplexed monoatomic hydrogen with a donor level above the mid band gap. Hydrogen‐boron pairing explains qualitatively the boron acceptor concentration profiles in hydrogen‐neutralized, p‐type silicon.

Schottky barrier diodes on 3C‐SiC

Abstract: Schottky barrier contacts have been made on n‐type 3C‐SiC epitaxially grown by chemical vapor deposition, and their characteristics were studied by the capacitance and photoresponse measurements. By evaporating Au onto chemically etched surfaces of 3C‐SiC, good quality Schottky barrier junctions have been obtained. The barrier height determined by the capacitance measurements is 1.15 (±0.15) eV, while the height by the photoresponse measurements is 1.11 (±0.03) eV. These values are about a half of the energy band gap Eg at room temperature.

Forward I‐V plot for nonideal Schottky diodes with high series resistance

Abstract: In this work we present an extension of Norde’s forward I‐V plot. This modified method allows us to obtain reliable values for three different parameters (n, R, and Is) in nonideal Schottky barrier diodes with high series resistance.

Recent models of Schottky barrier formation

Abstract: Two recent models of Schottky barrier formation are discussed. These invoke ‘‘metal‐induced gap states’’ or native defects to explain Fermi‐level pinning. Available experimental data can be satisfactorily explained by states intrinsic to the surface and interface, without postulating a defect pinning mechanism. In contrast, recent theoretical and experimental work appears to contradict the proposed defect mechanism. The connection between Schottky barriers and semiconductor heterojunction band lineups is proposed as a possible test of theory.

Electrical study of Schottky barrier heights on atomically clean and air‐exposed n‐InP(110) surfaces

Abstract: We report here a systematic study of the electronic properties of Schottky barrier diodes fabricated on atomically clean, as well as air‐exposed n‐InP (110) surfaces. Using the current‐voltage (I‐V) measuring technique, we found the barrier heights of 0.33 eV for Ni, Al, Sn, Mn, 0.43 eV for Pd, Cu, Au, Cr, and 0.54 eV for Ag. Contrary to earlier reports based on a limited amount of data, the results of this study do not show a simple relationship between the chemical reactivity and the Schottky barrier height. The large differences between the electrical characteristics of diodes prepared on clean surfaces and those prepared on air‐exposed surfaces were also not found.

Gap states in phosphorus-doped amorphous silicon studied by isothermal capacitance transient spectroscopy

Abstract: An application of the isothermal capacitance transient spectroscopy (ICTS) technique to a study of gap states in P-doped a-Si: H, as well as characteristics of a-Si: H Schottky barrier diodes used in the ICTS measurement, is described in detail. It is demonstrated that the electron-capture cross-section or the pre-exponential factor of the thermal emission rate of electron from gap states in a-Si: H can be determined, separating a temperature dependence from an energy dependence. On the basis of these advantages, the gap state profile g(E) in P-doped a-Si: H is measured precisely; the gap state bump associated with doubly-occupied dangling bonds is found to be located at 0·52 eV below E c It is also indicated that a multiphonon emission process with weak electron-phonon coupling predominates in the carrier-capture process at these states.

Electrical properties of CdTe films and junctions

Abstract: Polycrystalline films of CdTe have been deposited on graphite substrates, and homoepitaxial films on single‐crystal CdTe:P substrates, with hole densities as high as 1.5×1016 cm−3 without intentional doping of the films, using close‐spaced vapor transport. The dependence of hole density in the films on the properties of the source, the properties of the substrate, the growth rate, and the substrate temperature, indicates that the doping of the films is the result of a complex interaction between out‐diffusion of mobile impurities (if present) from the substrate and intrinsic defects. The capacitance‐versus‐voltage‐indicated hole density decreases slowly with time under a Schottky barrier, but not at a free film surface or under a CdS/CdTe heterojunction. CdS/CdTe solar cells have been prepared using these films, with solar efficiencies greater than 6%. The junction properties of CdS/CdTe heterojunctions are compared with those of In/CdTe Schottky barriers as a function of temperature; transport is dominat...

Sodium-tungsten bronze thin films I. Optical properties of dilute bronzes.

Abstract: Measurements of the electrical properties of polycrystalline Na x WO3 thin films in the range 0

Resonant tunneling transistors with controllable negative differential resistances

Abstract: Three-terminal devices based on resonant tunneling through two quantum barriers separated by a quantum well are presented and analyzed theoretically. Each proposed device consists of a resonant tunneling double barrier heterostructure integrated with a Schottky barrier field-effect transistor configuration. The essential feature of these devices is the presence, in their output current-voltage ( I_{D} - V_{D} ) curves, of negative differential resistances controlled by a gate voltage. Because of the high-speed characteristics associated with tunnel structures, these devices could find applications in tunable millimeter-wave oscillators, negative resistance amplifiers, and high-speed digital circuits.

A microscopic model of metal–semiconductor contacts

Abstract: A one‐dimensional local‐density model of the charge density,electrostatic potential, and energetics of metal–semiconductor contacts is constructed. This model is an extension of analogous models of bimetallic junctions to include the gap in the semiconductor excitation spectrum, space charge effects in the semiconductor, and fabrication‐induced charges near the interface. Self‐consistent analysis of the valence‐electron charge redistribution at the model metal–semiconductor interface relative to the corresponding vacuum surfaces reveals a cancellation which makes the height of the rectifying Schottky barrier directly proportional to the observed vacuum work function of the metal in the absence of additional charges induced by atomic relaxations or chemical reactions which occur during the fabrication of the interface. The experimentally observed stability of the Schottky barrier heights against changes is applied bias and semiconductor doping are predicted correctly. The occurrence of interfacial atomic rearrangements and/or chemical reactions is incorporated into the model via the inclusion of charge centers near the interface. Four types of centers are considered: donors, acceptors, and three‐state centers with both positive (U>0) and negative (U<0) effective electron–electron interactions. Applications of the model to describe measured barrier heights on GaSe(0001) and GaAs(110) require approximately 101 4 negative‐U centers per cm2 except in the case of noble metals and Sn on GaSe(0001).

Single crystal silicide silicon interfaces: Structures and barrier heights

Abstract: The atomic structures and the Schottky barrier heights of single crystal silicide–silicon interfaces were studied. Epitaxial NiSi2 and CoSi2 were grown under ultrahigh vacuum conditions on (111), (100), and (110) surfaces of Si. Lattice imaging by high resolution transmission electron microscopy allowed modeling of the interface atomic structures. Capacitance–voltage and current–voltage characteristics of these interfaces were studied. A dependence of barrier heights on orientation is observed which favors intrinsic mechanisms for their formation. The advantages of the present single crystal metal–semiconductor interfaces over the usual polycrystalline junctions in the study of Schottky barrier formation are demonstrated.

Direct variation of metal‐GaAs Schottky barrier height by the influence of interface S, Se, and Te

Abstract: The electrical properties and interface chemistry of Schottky barrier contacts (Ag, Al, Au, Mn, Pd, and Ti) formed on n-type GaAs (100) surfaces that had prior exposure to elemental S, Se, and Te are compared to those of ideal (metal deposited onto a clean surface) contacts. The interface Fermi energy E i Fand interface chemistry during contact formation were investigated by x-ray photoemission spectroscopy; the accompanying Schottky barrier height φ R was measured by current-voltage and capacitance-voltage techniques. A substantial decrease in φ B (and correlated change in Ei F) for Al and Mn contacts is associated with a contact metal-chalcogen chemical reaction at the Schottky barrier interface, while some nonreactive noble metal-chalcogen interfaces have a φ B increase. By choice of contact metal and interface chalcogen a φ B range of > 0.6 eV is obtained (∼ 0.35 to 1.0 eV, which is > 40% of the GaAs band gap) via corresponding changes in Ei F.

Schottky barriers on atomically clean n‐InP (110)

Abstract: We report the results of a systematic study of the Schottky barrier heights on n‐type InP (110). The measurements were performed on thick diodes and thin metal overlayers grown at room temperature under ultrahigh vacuum conditions on cleaved surfaces. A large number of metals, ranging from strongly reactive Ni, Al, Cr, Mn, and Pd to less reactive or nonreactive Ag, Au, Cu, Ga, and Sn have been used to correlate the barrier height with the interfacial chemistry. The barrier heights have been determined using the current‐voltage characteristics of diodes and the band bending related shifts in the core level spectra for the thin overlayers. Soft x‐ray photoemission spectroscopy has also been used to characterize the chemical reactions on a microscopic scale during the initial stages of the interface formation. Our results show several notable exceptions from the systematics relating the barrier heights with the interfacial chemistry. These results provide a critical test of currently considered models of Sch...

Broadband Y‐branch electro‐optic GaAs waveguide interferometer for 1.3 μm

Abstract: Electro‐optic Mach–Zehnder rib waveguide interferometers with low loss Y branches and Schottky barrier electrodes have been fabricated in n−/n+‐GaAs by reactive ion etching. With antireflection coating and optimized Y branches device losses of the interferometers at 1.3 μm were as low as 4 dB. In a push‐pull configuration drive voltages of only 13 V suffice to attain a modulation depth of 12.7 dB. The optical signal bandwidth of these interferometers was measured to exceed 4.5 GHz.

The Bethe condition for thermionic emission near an absorbing boundary

Abstract: The Bethe condition for thermionic emission in Schottky diodes is analysed in terms of the transport of carriers near the top of an absorbing barrier, under forward bias. It is shown that the usually accepted values of the drift velocity vs and of the carrier density n(0) at the barrier maximum are not correct, vs being underestimated by a factor of 2, and n(0) being overestimated by about the same factor. Fortunately, these discrepancies compensate in the product n(0)vs, which yields the correct forward current. It is shown also by means of examples that the Bethe condition is satisfied only over a relatively limited range.

Semiconductor integrated circuit vertical geometry impedance element

Abstract: A resistive load element comprises a Schottky barrier metal layer formed on the top surface of a doped p-type polycrystalline silicon (polysilicon) plug contacting a surface n+ zone located in a semiconductor body at a major horizontal surface thereof. The Schottky barrier metal layer is advantageously essentially a metal compound, such as titanium nitride, which does not react with the polysilicon and which forms a Schottky barrier contact with the polysilicon top surface of the plug. The polysilicon plug extends vertically down to the n+ zone through an aperture in an insulating layer that coats the major surface of the semiconductor body. The top surface of the Schottky barrier layer is coated with another metal layer, such as aluminum, for interconnection purposes. A pair of such elements can be integrated as loads, for example, in a static random access memory ("flip-flop") cell.

Influence of S and Se on the Schottky‐barrier height and interface chemistry of Au contacts to GaAs

Abstract: The electrical properties and interface chemistry of Au Schottky‐barrier contacts formed on n‐type GaAs (100) surfaces that had prior exposure (at room temperature) to elemental S or Se are compared to those of Au contacts to clean surfaces (ideal contacts). The interface Fermi‐level energy EiF and chemistry during contact formation were investigated by x‐ray photoemission spectroscopy (XPS). The Schottky‐barrier height φB was measured by current‐voltage and capacitance‐voltage methods on the same interfaces characterized by XPS. The exposure of clean GaAs to elemental S or Se results in formation of a ∼5 A surface layer of Ga and As chalcogenides via a limited chemical reaction. The Schottky‐barrier height for Au contacts to the S or Se exposed surfaces had a 0.2 eV variation (0.8–1.0 eV) centered about the φB=0.89 eV value for the ideal Au contact. Changes in EiF over a ∼0.4 eV range occur in response to changes in interface chemistry during surface treatment sequences that include S and Se exposure and...

Schottky barrier height measurements of epitaxial NiSi2 on Si

Abstract: Photoresponse measurements of the Schottky barrier heights of epitaxial NiSi2 layers on nondegenerate n‐(111) Si, for type‐A and type‐B orientations, have been performed. The type‐A and type‐B cases are consistently observed to differ in barrier height by greater than 0.1 eV. We obtain measured values for φB0 (at T=300 K) of 0.62±0.01 eV and 0.77±0.05 eV for type A and B, respectively.

Dangling bonds and Schottky barriers

Abstract: We review theoretical interpretations of Schottky barriers and Fermi‐level pinning, which result when metals and other chemical species are deposited on semiconductor surfaces. Experiments indicate that these two phenomena are closely connected, so a theory of Schottky barriers must also explain Fermi‐level pinning for submonolayer coverages of both metallic and nonmetallic species. Proposed mechanisms include the following: (a) Intrinsic surface states. For GaAs and several other materials, there are no intrinsic surface states within the band gap; GaP, e.g., does have surface states in the gap, but they are not at the correct energy to explain Schottky barrier formation. (b)Metal‐induced gap states. These states, which require a thick metal overlayer, cannot explain Fermi‐level pinning at submonolayer metallic coverages. They also cannot explain why a single semiconductor (n‐type InP) exhibits two distinct Schottky barrier heights. Furthermore, they cannot explain why the Schottky barrier persists when ...

Charge collection in a Schottky diode as a mixed boundary-value problem

Abstract: An analysis is given of the determination of bulk diffusion lengths in semiconductors from the induced current profiles that are obtained by scanning an electron beam with normal incidence on a Schottky diode. The discussion assumes that the carrier recombination velocity at the free semiconductor surface is vs = 0. In this case the mixed boundary conditions of the diffusion problem for excess minority carriers can be converted into normal ones by using polar coordinates, and an explicit expression for the induced current profile can be given. This expression is compared to that already known for the opposite case vs = ∞, to establish the influence of the surface recombination velocity on a number of profile properties, such as symmetry, asymptotic decay, or low-order moments of the derivative. It is shown that by evaluating the variance of the profile derivative at two beam energies the diffusion length can be determined independently of the knowledge of the value of vs.

Comment on “Theory of semiconductor heterojunctions: The role of quantum dipoles”

Abstract: Tersoff’s heterojunction model is critically analyzed using extensive experimental data obtained from photoemission measurements of the valence-band discontinuity.

Schottky Diodes and Ohmic Contacts for the III-V Semiconductors

Abstract: In this chapter a review of the electrical properties of metal-semiconductor contacts to the III-V semiconductors is given. Metal-semiconductor structures play an important role in devices based on the III-V compound semiconductors in the form of Schottky-barrier diodes or ohmic contacts. Important III-V devices utilizing Schottky-barrier junctions include solar cells, microwave mixer diodes, and metal semiconductor field-effect transistors (MESFETs) and their associated integrated circuits. Schottky diodes also find widespread use for III-V semiconductor materials characterization, including carrier concentration profiling and deep-level identification. Ohmic contacts with low resistance are necessary for high performance in many III-V devices. For example, the efficiency of light-emitting diodes and lasers is strongly influenced by contact resistance, and the noise behavior and the gain of an FET are significantly affected by the character of ohmic contacts. In all of these cases, the metal-semiconductor interface is formed on a chemically etched, as compared to an atomically clean, semiconductor surface. Thus, in this chapter the properties of Schottky diodes and ohmic contacts prepared by chemically etching the III-V semiconductors are emphasized, while the previous chapter dealt with metal-semiconductor interface formation on atomically clean surfaces.

Interface potential changes and Schottky barriers

Abstract: By investigating local potential changes at the Si(111)/Al interface, we find restrictions on the use of “canonical” Schottky-barrier heights. It is demonstrated that the “metallic” behavior of the metal-induced gap states is insufficient to completely screen out stronglocal interface potential effects on Schottky-barrier heights.