Variation Of Barrier Height Research Articles

Contactless measurement of Schottky barrier heights using secondary electrons

A contactless technique using electron-beam-induced voltage has been developed to measure the barrier heights of Schottky diodes. The method detects the change in the on-set energy of the secondary electrons using a cylindrical mirror analyzer in a scanning Auger microprobe (SAM). Measurements have been carried out in a Si diode with half-high-barrier (platinum) and half-low-barrier (titanium) height metal coverage in order to establish the correlation between the measured energy change to the difference in the barrier heights. Using an electron beam of about 1-μm diameter, a change in the on-set energy of 50 meV can be detected with a lateral resolution of about 1 μm. The fine-beam Auger capability of the SAM enables us to identify in situ the local chemistry change responsible for the barrier height variation. This provides a technique with high spatial and energy resolution for investigating the correlation between the interface chemistry and electrical properties of mixed diodes.

Are interface states consistent with Schottky barrier measurements?

Many Schottky barrier heights have less dependence upon metal work function than the simple work function matching model of this interface proposed by Schottky 40 years ago. The conventional explanation for this result involves the assumption that interface states of high density change their occupancy in response to work function differences and thereby reduce the variation of Schottky barrier heights. Such states could also change their occupancy under bias variations, and transport measurements have been interpreted in this fashion. We show that these latter assumptions also imply that the Schottky barrier height should itself be strongly altered by bias—a conclusion inconsistent with the results of capacitance and current transport experiments.

Electron beam study of silicide Schottky diodes

An electron-beam-induced voltage (EBIV) technique has been developed to measure the barrier height of Schottky diodes. The principle of this technique is described and is compared with the conventional electron-beam-induced current (EBIC) technique. Applications of both techniques are illustrated in a study of composite silicide Schottky diodes with mixed high and low barrier areas formed using bilayer and co-evaporated PdTi and PtTi films on silicon substrates. The difficulty of using EBIC for quantitative studies of diode characteristics is discussed and contrasted with the advantages of the EBIV technique. The extension of the EBIV technique to contactless measurements of barrier height variation with good lateral resolution is described.

Sur l'utilisation des modifications de barrière de surface avec la température pour caractériser les états de surface

This paper deals with the determination of the density and the energy level of semiconductor surface states from the variations in the surface barrier height with temperature in the range 100–400 K. Examples of calculations for discrete energy level states are given.

The Al-(n-InP) Schottky barrier

Schottky barriers have been prepared by the evaporation of aluminium on to bulk-grown n-type InP slices. Reproducible devices were obtained providing sufficient care was taken over the preparation of the semiconductor surface. Current-voltage, capacitance-voltage and photocurrent measurements were made on the diodes. The current measurements showed the ideality factor n, to be close to unity at room temperature and above, indicating that the main mechanism of current flow was thermionic emission. Below room temperature, the ideality factor increased. The capacitance measurements indicated the presence of a deep donor about 1 eV below the conduction band edge. All three measurement techniques gave a calculated value of Schottky barrier height in the region of 0.5 eV. The variation of barrier height with temperature was found to be 4*10-4 eV K-1, which corresponds closely with the temperature variation of the band-gap of InP.

Ag versus Pb electrodes in inelastic-electron-tunneling spectroscopy

The elastic and inelastic tunneling characteristics for Ag and Pb electrodes on Al-$\mathrm{Al}{\mathrm{O}}_{x}$ substrates doped with a series of aromatic carboxylic acids have been compared. Model calculations of barrier heights and measurements of \ifmmode\pm\else\textpm\fi{} bias asymmetries in tunnel characteristics and inelastic-electron-tunneling (IETS) mode intensities have been compared. Ag-overlaid electrodes produce a systematic lowering of the effective organic barrier heights by a factor of \ensuremath{\sim}2 and enhance the nonlinear characteristics of the junction. The large relative variation in effective barrier heights for specific carboxylic acids previously observed for Pb electrodes is also observed for Ag. For effective barrier heights \ensuremath{\le} 1 eV, the loss of IETS mode intensity at high bias voltages is accentuated by Ag. The \ifmmode\pm\else\textpm\fi{} bias asymmetry in IETS mode intensity for Ag is also less than predicted by the long-range molecular interaction potential, in contrast to the agreement with the long-range potential observed for Pb.

Tests of collinear quasiclassical trajectory transmission coefficient correction to transition state theory

We test the accuracy of a collinear quasiclassical trajectory transmission coefficient correction to conventional transition state theory. Comparisons are made between the so-modified transition state theory, conventional transition state theory, and previously reported three dimensional quasiclassical trajectory rate constants for several reactions. They are the O(3P)+H2(ν = 0), H2(ν = 1) reactions on three different potential energy surfaces, the F+H2(ν = 0) reaction on the LEPS surface of Muckerman (no. 5), and the H+H2(ν = 0) reaction on the Porter–Karplus surface. Although each of these systems has a collinear transition state, they span a wide variation in saddle point location and classical barrier height. We find that the collinear quasiclassical trajectory transmission coefficient very successfully corrects the conventional transition state rate constant even for the O(3P)+H2(ν = 1) reaction where the latter differs from the 3D quasiclassical one by two orders of magnitude.

Structures and decay dynamics of thiocarbonyl excited states

Gas phase absorption, emission and emission excitation spectra have provided detailed ground and excited state structural information for several representative small thiocarbonyls. The ground states are planar but the excited states are generally non-planar and may exhibit a large variation in inversion barrier heights and equilibrium out-of-plane angles. The CS bond is elongated in excited states, by as much as 0.5 Å in the S 2 1(π,π*) states of Cl 2CS and ClFCS. Tetra-atomic thiocarbonyls appear to decay solely by radiative means from bound levels of their S 1 1(n,π*) states under collision-free conditions; radiative decay of the corresponding T 1 states has not been observed. Excitation to low-lying vibrational levels of the S 2 states of ClFCS and Cl 2CS in the gas phase results in S 2 → S 0 emission with high quantum yields (ϕ f → 1.0). At higher vibrational energies non-radiative decay (probably leading to dissociation) dominates. The observation of intense emission from S 2 has been exploited to probe the mechanisms of the two-photon absorption in gas phase Cl 2CS. Sequential two-photon absorption via T 1 ▪ and bimolecular singlet—singlet energy pooling ▪ have been observed.

Electron Beam Study of Silicide Schottky Diodes

An electron-beam-induced voltage (EBIV) technique has been developed to measure the barrier height of Schottky diodes. The principle of this technique is described and is compared with the conventional electron-beam-induced current (EBIC) technique. Applications of both techniques are illustrated in a study of composite silicide Schottky diodes with mixed high and low barrier areas formed using bilayer and co-evaporated Pd-Ti and Pt-Ti films on silicon substrates. The difficulty of using EBIC for quantitative studies of diode characteristics is discussed and contrasted with the advantages of the EBIV technique. The extension of the EBIV technique to contactless measurements of barrier height variation with good lateral resolution is described.

The variation of Schottky barrier height due to an interfacial layer

Various types of modified structure that are possible because of the presence of an interfacial layer between a metal and an n-type semiconductor are discussed by considering the typical case of aluminium metallization. An attempt is made to estimate the barrier height ø B theoretically in each case. The Al/n-GaAs contact with an interfacial semiconductor layer can give a high Schottky barrier junction having a thin interfacial layer of low resistivity and high optical transparency.

Interpretation theorique de la reaction de diels-alder dans la serie des dienes fonctionnels dissymetriquement substitues-II : Etude des mecanismes de reaction par calcul mindo des etats de transition

The different behaviour of two 1- or 2-ethoxy butadiene isomers with respect to acrolein in the Diels-Alder reaction is explained on the basis of reaction mechanisms. Using MINDO/2 calculations, various models of the transition state are investigated and geometric parameters for each reaction path coordinate are optimized. The choice of a model describing the transition state is given by the corresponding potential barrier height, which characterizes the approach of reagents and the site of the functional of the diene. Its lowest value corresponds to a concerted reaction mechanism with acrolein; a synchronous mechanism is found for 2-ethoxy butadiene, and a two-stage one for 1-ethoxy butadiene. The variation in barrier height in the two systems is well correlated with the corresponding change in the observed reaction rate.

Material reactions and barrier height variations in sintered AlInP Schottky diodes

Significant increases in the AlInP Schottky barrier have been obtained by process modification of the metal-semiconductor interface. The resultant barrier height increases (from 0.3 to 0.6 eV) are due to oxygen build-up at the interface, in the form of P 2O 5. Auger electron spectroscopy studies of the metal-semiconductor interface indicate an excellent correlation between barrier height increases and oxygen build-up at the AlInP interface.

Stress effect of Ag—n-type Si Schottky-barrier diode

The uniaxial stress effect on Ag-n-type Si Schottky-barrier diodes was examined. The simple barrier height variation could not explain the observed results of the current increment in both forward and reverse <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J- V</tex> characteristics (particularly the absence of saturation current in the reverse-biased region) and the constant barrier height obtained from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C-V</tex> measurement under pressure. It was found that application of pressure effectively diminishes the potential barrier height, affecting only the electrons contributing to current transport. Its effect can be expressed by introduction of the stress-sensitive length x <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> . Experimental results show that x <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> is proportional to the applied pressure.

Behavior of Au/InP Schottky diodes under heat treatment

Variations of barrier heights with heat treatment are observed on Au/(n-type) InP Schottky diodes. The n-type InP wafers used are vapor epitaxially grown ({100} face oriented) and have carrier concentrations in the range 4×1015 to 2×1016 cm−3. Before the deposition of the metal, the surfaces are chemically etched in a bromine-methanol mixture. Electrical characteristics are reported as a function of isochronous heating cycles from 120 to 340 °C, using conventional Schottky barrier I-V and C-V analysis. The barrier heights are in the range 0.42–0.49 eV. Degradation characteristics and decreased barrier heights are observed after a 340 °C heat treatment in N2 with a residual O2 atmosphere. Distribution profiles of elemental species obtained by Auger electron spectroscopy associated with an Ar+-ion-beam sputtering show the interdiffusion between the metal and InP as a function of the heat treatment: out-diffusion of In and O as a solid solution of In2O3 in the Au film and Au and O diffusion through the Au/InP interface at 340 °C.

Variation of Pt Si-nSi Barrier Height with Fabrication Parameters, and Characterisation of the Electrical Behaviour of the Junction

Photoelectric barrier height measurements of the PtSi-nSi junction are reported for varying fabrication parameters. These include crystal orientation, sputter-etch procedures, thickness of the deposited metal layer, crystal resistivity. Variations up to ≃ 0.1 eV are found and crystal orientation has the largest influence. Deviations from the ideal IV-characteristics for the junctions are reported.The diode saturation current (as derived from forward characteristics) varies two orders of magnitude over the wafer resistivity range 0.1-500 Ω-cm. This agrees with expectations from numerical integration of the transport equation in the depletion region. This variation is usually not considered in the treatment of Schottky diodes but is larger than, e.g., effects due to quantum reflection and phonon collisions at the barrier.

Theory of semiconductor surface states and metal–semiconductor interfaces

The electronic structure of vacuum–semiconductor and metal–semiconductor interfaces has been studied using a method involving self-consistent pseudopotentials. Our model for an intimate metal–semiconductor interface consists of jellium in contact with a semiconductor described in the pseudopotential formalism. Local density of states and charge densities are used to analyze the electronic properties of the two types of interfaces. For the vacuum–semiconductor case, Si (111) surfaces and the (110) surfaces of III–V and II–VI zincblende semiconductors are investigated, with GaAs and ZnSe considered as zincblende prototypes. For metal–semiconductor interfaces, jellium of Al density in contact with (111) surfaces of Si and the (110) surfaces of GaAs, ZnSe, and ZnS are investigated. The calculated Schottky barrier heights are in good agreement with experimental results. It is shown that the variations in the experimental barrier height for different metals in contact with various semiconductors can be understood in terms of a simple model using the result of the pseudopotential calculations. The relation of our results to other theories and current experiments is discussed.

The nature of barrier height variations in alloyed Al-Si Schottky barrier diodes

The nature of barrier height variations in alloyed Al-Si Schottky barrier diodes

Far infra-red absorption of disubstituted propanes in rotator, solid and liquid phases

Experimental observations of the far infra-red (f.i.-r.) absorption spectra of three polar di-substituted propanes (2,2-dichloro-, 2-chloro-2-nitro-, 2-methyl-2-nitro-propane) over the temperature range 133–303 K in the liquid, rotator and non-rotator solid phases are reported. The spectra in both the liquid and rotator phases are discussed in terms of two simple theoretical models of librational and relaxational motions: an acceptable fit to the experimental spectra is obtained on the basis of reasonable barriers and other parameters of the molecular motion. One of the models indicates that the molecular librational potential wells may become narrower with decreasing temperature and that there may be a distribution of potential well depths or shapes. The variation of potential barrier height with group substitution is also discussed.

Determination of the surface barrier height by combined measurements of surface photovoltage and field effect

A new technique is described for determining the surface barrier height in large-gap semi-conductors. Field effect induced variations of the surface barrier height are picked up by superimposed surface photovoltage measurements. The magnitude of the electric field which causes the flattening of the energy bands is determined and used to calculate the surface barrier height in equilibrium.

Schottky barriers on p-type silicon

Measurements have been made of the electrical characteristics of Schottky barriers made by evaporating films of various metals (Al, Pb, Ni, Au, Ag, Cu) onto p-type silicon. The barriers were generally lower than on n-type silicon, and in the case of Au the barrier was so low as to provide an effectively ohmic contact at room temperature. The truly exponential portion of the forward I– V characteristic was restricted to a comparatively small voltage range. Within this range ‘ n’ values of about 1.10 were obtained. The reverse characteristics could be explained in terms of generation in the depletion region. The variation of barrier height with metal work-function indicates that the surface-state parameters (density of states and position of neutral level) are essentially the same for p-type as for n-type silicon. This is confirmed by the fact that, for a given metal, the sum of the barrier heights on n-type and p-type silicon is approximately equal to the band-gap.