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The energetic resolution of Schottky barrier visualization is determined by utilizing differences in interface band structures between the Au/Si(001) and Au/Si(111) non-epitaxial interfaces and parallel momentum conservation of the carriers. The visualization technique is based on ballistic electron emission microscopy and spectroscopy, where tens of thousands of spectra are collected on a grid and then fit to extract a spatially resolved map and histogram of the electrostatic barrier height. A resolution of 10 meV is determined from the minimal splitting and eventual merging of the histograms as the gold thickness decreases for the Au/Si(001) and Au/Si(111) samples. This splitting is below previously measured differences in barrier heights extracted from computational modeling of measured barrier height distributions from other interfaces.

Ab initio nonequilibrium Keldysh formalism based on an $N$-order renormalization technique is used to compute $I(V)$ ballistic electron emission microscopy characteristics at the Au/Ge(001) interface. Such a formalism quantitatively reproduces precise experimental measurements under ultrahigh vacuum and low-temperature conditions. At $T=0$ K, the ballistic current follows the law ${(V\ensuremath{-}{V}_{\mathrm{SB}})}^{2.1}$, ${V}_{\mathrm{SB}}$ being the Schottky barrier. At $Tg0$ K, temperature effects become significant near the onset and must be taken into account to identify an accurate value for ${V}_{\mathrm{SB}}$ from a best-fit procedure. We find two values for ${V}_{\mathrm{SB}}$, 0.67 and 0.75 eV, which we associate with two different atomic registries at the interface.

We have developed a calculation scheme for the elastic electron current in ultra-thin epitaxial heterostructures. Our model uses a Keldyshs non-equilibrium Greens function formalism and a layer-by-layer construction of the epitaxial film. Such an approach is appropriate to describe the current in a ballistic electron emission microscope (BEEM) where the metal base layer is ultra-thin and generalizes a previous one based on a decimation technique appropriated for thick slabs. This formalism allows a full quantum mechanical description of the transmission across the epitaxial heterostructure interface, including multiple scattering via the Dyson equation, which is deemed a crucial ingredient to describe interfaces of ultra-thin layers properly in the future. We introduce a theoretical formulation needed for ultra-thin layers and we compare with results obtained for thick Au(1 1 1) metal layers. An interesting effect takes place for a width of about ten layers: a BEEM current can propagate via the center of the reciprocal space (I) along the Au (1 1 1) direction. We associate this current to a coherent interference finite-width effect that cannot be found using a decimation technique. Finally, we have tested the validity of the handy semiclassical formalism to describe the BEEM current., This work has been supported by the MINECO (MAT-2014/54231-C4-1-P and MAT-2014/59966/R), the EU (ERC-2013-SYG-610256), and the program Maria de Maeztu (MDM/2014/0377).

Oxide-free Si and Ge surfaces have been passivated and modified with organic molecules by forming covalent bonds between the surfaces and reactive end groups of linear alkanes and aromatic species using single-step deposition in supercritical carbon dioxide (SCCO2). The process is suitable for large-scale manufacturing due to short processing times, simplicity, and high resistance to oxidation. It also allows the formation of monolayers with varying reactive terminal groups, thus enabling formation of nanostructures engineered at the molecular level. Ballistic electron emission microscopy (BEEM) spectra performed on the organic monolayer on oxide-free silicon capped by a thin gold layer reveals for the first time an increase in transmission of the ballistic current through the interface of up to three times compared to a control device, in contrast to similar studies reported in the literature suggestive of oxide-free passivation in SCCO2. The SCCO2 process combined with the preliminary BEEM results opens up new avenues for interface engineering, leading to molecular electronic devices.

Density of states is studied by a ballistic electron emission microscopy/spectroscopy on self-assembled InAs quantum dots embedded in GaAs/AlGaAs heterostructure prepared by metal–organic vapor phase epitaxy. An example of integral quantum dot density of states which is proportional to superposition of a derivative of ballistic current–voltage characteristics measured at every pixel (1.05 nm×1.05 nm) of quantum dot is presented. For the two lowest observed energy levels of quantum dot (the maxima in density of states) the density of states is mapped and correlated with the shape of quantum dot. It was found that prepared quantum dots have a few peaks on their flatter top and a split of the lowest energy level can be observed. This effect can be explained by inhomogeneous (nonuniform) stress distribution in the examined quantum dot.

By preparing phenyl-terminated monolayers on hydrogen-terminated silicon (111), we show that their higher surface densities in comparison with n-alkyl monolayers improves their electrical properties (lower reverse-bias currents, higher effective barrier heights, and closer-to-unity ideality factors) when contacted using either mercury drop or thermally deposited gold electrodes. Consistent with these macroscopic results, the ballistic electron emission microscopy characterization shows a significant decrease in ballistic current and higher local barrier height for the phenyl-terminated monolayers, when compared with gold | n-alkyl monolayer | silicon junctions. We propose that increased intermolecular interaction through π–π stacking of the phenyl head-groups stabilizes the monolayer structure at the buried interface and inhibits the penetration of thermally deposited gold atoms.

We use ballistic electron emission microscopy to investigate prototypical Au/Nb-doped SrTiO3 (NSTO) Schottky barrier diodes for different temperatures and doping levels. To this end, ultrathin Au overlayers are thermally evaporated onto TiO2-terminated NSTO single crystal substrates. We show that at room temperature, regardless of the nominal doping, rectification is controlled by a spatially inhomogeneous Schottky barrier height (SBH), which varies on a length scale of tens of nanometers according to a Gaussian distribution with a mean value of 1.29–1.34 eV and the standard deviation in the range of 80–100 meV. At lower temperatures, however, doping effects become relevant. In particular, junctions with a low Nb content of 0.01 and 0.05 wt. % show an ∼300 meV decrease in the mean SBH from room temperature to 80 K, which can be explained by an electrostatic analysis assuming a temperature-dependent dielectric permittivity for NSTO. In contrast, this model fails to predict the weaker temperature dependence of SBH for junctions based on 0.5 wt. % NSTO. Our nanoscale investigation demands to reassess conventional models for the NSTO polarizability in high-intensity electric fields. Furthermore, it contributes to the comprehension and prediction of transport in metal/SrTiO3 junctions and devices.

The electrostatic barrier at a metal semiconductor interface is visualized using nanoscale spatial and meV energetic resolution. A combination of Schottky barrier mapping with ballistic electron emission microscopy and computational modeling enables extraction of the barrier heights, the hot electron scattering, and the presence of localized charges at the interface from the histograms of the spectra thresholds. Several metal semiconductor interfaces are investigated including W/Si(001) using two different deposition techniques, Cr/Si(001), and mixed Au-Ag/Si(001). The findings demonstrate the ability to detect the effects of partial silicide formation in the W and Cr samples and the presence of two barrier heights in intermixed Au/Ag films upon the electrostatic barrier of a buried interface with nanoscale resolution. This has potential to transform the fundamental understanding of the relationship between electrostatic uniformity and interface structure for technologically important metal semiconductor interfaces.The electrostatic barrier at a metal semiconductor interface is visualized using nanoscale spatial and meV energetic resolution. A combination of Schottky barrier mapping with ballistic electron emission microscopy and computational modeling enables extraction of the barrier heights, the hot electron scattering, and the presence of localized charges at the interface from the histograms of the spectra thresholds. Several metal semiconductor interfaces are investigated including W/Si(001) using two different deposition techniques, Cr/Si(001), and mixed Au-Ag/Si(001). The findings demonstrate the ability to detect the effects of partial silicide formation in the W and Cr samples and the presence of two barrier heights in intermixed Au/Ag films upon the electrostatic barrier of a buried interface with nanoscale resolution. This has potential to transform the fundamental understanding of the relationship between electrostatic uniformity and interface structure for technologically important metal semiconductor ...

Ballistic electron emission microscopy has been utilized to investigate the hot-electron transport properties of the Ag/Si(001) Schottky diode utilizing metal films deposited both in situ and ex situ. The Schottky barrier heights are measured to be 0.57±0.02 and 0.59±0.02 eV for the ex situ and in situ depositions, respectively. The metal overlayers demonstrate typical Volmer–Weber growth when deposited on the Si(001) semiconducting substrate, as seen in the scanning tunneling microscopy images. An enhancement in hot-electron transmission is measured for the in situ deposited metal films when compared to the ex situ films.

Ballistic electron emission microscopy (BEEM) has been used to study the processes affecting electron transport along the [0001] direction of finite layer MoS2 flakes deposited onto the surface of Au/Si(001) Schottky diodes. Prominent features present in the differential spectra from the MoS2 flakes are consistent with the density of states of finite layer MoS2 calculated using density functional theory. The ability to observe the electronic structure of the MoS2 appears to be due to the relatively smooth density of states of Si in this energy range and a substantial amount of elastic or quasi-elastic scattering along the MoS2/Au/Si(001) path. Demonstration of these measurements using BEEM suggests that this technique could potentially be used to study electron transport through van der Waals heterostructures, with applications in a number of electronic devices.

This chapter contains sections titled: Overview Tunneling Theory Surface Structure Atomic Force Microscopy Ballistic Electron Emission Microscopy Atomic Positioning Summary

Ballistic electron emission microscopy (BEEM) and its spectroscopy utilize ballistic transport of hot carriers as a versatile tool to characterize nanometer-scale structural and electronic properties of metallic and semiconducting materials and their interfaces. In this review, recent progress in experimental and theoretical aspects of the BEEM technique are covered. Emphasis is drawn to the development of BEEM in several emerging fields, including spin-sensitive hot-carrier transport through ferromagnetic thin films and multilayers, hot-electron spectroscopy and imaging of organic thin films and molecules, and hot-electron induced electroluminescence in semiconductor heterostructures. A brief discussion on BEEM of cross-sectional semiconductor heterostructures and advanced insulator films is also included.

In this article, Au/titanylphthalocyanine/n-GaAs diodes incorporating ultrathin films of the archetypal organic semiconductor titanylphthalocyanine were investigated by ballistic electron emission microscopy/spectroscopy (BEEM/S). BEEM/S measurements were used to determine the transmission of ballistic electrons through titanylphthalocyanine as a function of energy and temperature. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; In the field of organic and molecular electronics at monolayer coverage, the need for abrupt and well-controlled top metal contacts is a key point. A general method which provides reliable molecular junctions with most metals remains to be found. In this paper we show that reliable molecular junctions Au/hexadecanethiol/n-GaAs(100) are obtained using buffer-layer-assisted growth (BLAG). They show in hot electron transport measurements at the nanoscale a tunnel regime through the organic monolayer with a full spatial uniformity. Using ballistic electron emission microscopy (BEEM) in the spectroscopic mode as well as photoemission and C(V)-transport measurements, we draw a coherent band alignment scheme of the whole heterostructure at the nanoscale and at the macroscopic scale. Through this study, the BLAG method appears as a general method that should work for contacting organic monolayers with most metals. © 2016 American Chemical Society.

In this article Au/titanylphthalocyanine/GaAs diodes incorporating ultra smooth thin films of the archetypal organic semiconductor titanylphthalocyanine (TiOPc) were investigated by Ballistic Electron Emission Microscopy/Spectroscopy (BEEM/S). Analyzing the BEEM spectra, we find that the TiOPc increases the BEEM threshold voltage compared to reference Au/GaAs diodes. From BEEM images taken we conclude that our molecular beam epitaxial (MBE) grown samples show very homogeneous transmission, compare to wet chemically manufactured organic films. The barrier height measured on the Au- TiOPc-GaAs is Vb ≈ 1.2eV, which is in good agreement with the data found in [T. Nishi, K. Tanai, Y. Cuchi, M. R. Willis, and K. Seki Chem. Phys. Lett., vol. 414, pp. 479-482, 2005.]. The results indicate that TiOPc functions as a p-type semiconductor, which is plausible since the measurements were carried out in air [K. Walzer, T. Toccoli, A. Pallaori, R. Verucchi, T. Fritz, K. Leo, A. Boschetti, and S. Iannotte Surf. Scie., vol. 573, pp. 346-358, 2004].

In this work, we present an investigation of the Pt and Pd-HfO2-p-Si interfaces using ballistic electron emission microscopy. The band alignment of the Pt-HfO2-p-Si structure is inferred. The potential drop in the oxide has been determined. Oscillations in the collector current with increasing bias enable estimation of the effective mass of electrons in HfO2 in the range of 0.35-0.44 m0. Stressing studies indicate modest resistance to stressing, with a threshold of 0.5 nC for damage to the base/oxide. Our work is the first successful application of the BEEM technique to metal-high K dielectric interfaces.

We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky barrier distribution over silver /H-T3-(CH2)4-HS (abbreviated as T3C4SH) self assembled monolayer interface area with nanometer scale spatial resolution. The selfassembled monolayer is absorbed on template stripped gold. BEEM images show spatially non-uniform carrier injection. A Wentzel Kramel Brillouin (WKB) calculation is performed and compared with BEEM spectra. The results show that the measured currents are four orders of magnitude larger than the direct tunnelling contribution, indicating molecular levels being accessed. To further substantiate the findings, characterization by STM distance versus potential spectroscopy is carried out to determine injection barriers at the interface. The results from these two techniques are compared and the implications of which will be discussed.

Ballistic electron emission microscopy (BEEM) is a new method by apply the spatial resolution capabilities of the scanning tunneling microscope (STM) to investigate electron transport properties in the quantum dots. This method requires three terminals: a sharp tip to inject electrons, a conductive layer and a semiconductor substrate. The transport-related properties of the sample can be obtained by using the characteristic of the injected and collected electrons. In this paper proposed a BEEM model for the silicon quantum dots (Si-QDs) on SiO2 layer prepared by LPCVD technique. SiO2 layer was thermally grown on p-type Si (100) wafer in dry O2 atmosphere and a thin gold layer cap used to provide a conductive layer on top of the Si-QDs for the BEEM characterization.

We study structural and electronic inhomogeneities in Metal—Organic Molecular monoLayer (OML)—semiconductor interfaces at the sub-nanometer scale by means of in situ Ballistic Electron Emission Microscopy (BEEM). BEEM imaging of Au/1-hexadecanethiols/GaAs(001) heterostructures reveals the evolution of pinholes density as a function of the thickness of the metallic top-contact. Using BEEM in spectroscopic mode in non-short-circuited areas, local electronic fingerprints (barrier height values and corresponding spectral weights) reveal a low-energy tunneling regime through the insulating organic monolayer. At higher energies, BEEM evidences new conduction channels, associated with hot-electron injection in the empty molecular orbitals of the OML. Corresponding band diagrams at buried interfaces can be thus locally described. The energy position of GaAs conduction band minimum in the heterostructure is observed to evolve as a function of the thickness of the deposited metal, and coherently with size-dependent electrostatic effects under the molecular patches. Such BEEM analysis provides a quantitative diagnosis on metallic top-contact formation on organic molecular monolayer and appears as a relevant characterization for its optimization.

We have analyzed the transfer efficiency of ballistic electron emission microscopy (BEEM), taking the finite spot size of the emitted electron beam from scanning probes into account. Three-dimensional diffraction from an aperture at a surface–metal/air interface is introduced to model an effect caused by the finiteness of spot size. As a general trend, the diffraction decreases BEEM transfer efficiency. The diffraction effect increases as the spot size decreases and the air-gap distance increases. In a Au/GaAs sample, BEEM transfer efficiency markedly deteriorates down to 6% of the value derived from a conventional planar tunneling theory when a spot size of 0.2 nm, an air-gap distance of 0.6 nm, and an electron energy of 0.2 eV, measured from the bottom of the GaAs conduction band, are assumed. BEEM transfer efficiency is markedly dependent on the spot size of the emitted hot electron. This result indicates that the BEEM current depends on the spatial resolution of the scanning probe, that is, the condition of the tip apex.

The nanometric localization of current transport in heterogeneous Schottky barriers was obtained by the combination of the electric field localization at the apex of a biased conductive atomic force microscopy (c-AFM) tip and of the metal films high-resistivity properties. An abrupt increase of the resistivity, modeled by a quantum-mechanical approach, was measured in Au thin films with a thickness below 10 nm. For Au ultrathin film resistivity, exceeding by two orders of magnitude the bulk value, the nanometric localization of the current transport occurs. This physical effect represents the basic principle of a microscopy approch for two-dimensional Schottky barrier height mapping, which is alternative to conventional ballistic electron emission microscopy ( BEEM). A spatial resolution in the order of the tip diameter ( 10 - 20 nm) is demonstrated by considering the realistic description of the system ( physical and geometrical). Schottky barrier inhomogeneities in a Au/4H-SiC system were imaged with an energy resolution better than 0.1 eV.

In this paper we describe how cross-sectional ballistic electron emission microscopy (XBEEM) can be used to measure the Schottky barrier height profile of a GaAs/AlGaAs multi heterostructure in cross-sectional geometry. By recording ballistic electron spectra across the heterostructure with a local resolution in the nm range, it is found that the measured Schottky barrier height profile is smeared out compared to the conduction band profile calculated from the sample growth parameters. We attribute this behavior to lateral band bending effects along the heterojunction. In addition, we have evidence that the barrier height profile is influenced by single impurities in the AlGaAs layers.

We describe the design and implementation of modifications to an ambient STM with a slip–stick approach mechanism to create a system capable of ballistic electron emission microscopy (BEEM) and spectroscopy (BEES). These modifications require building a custom sample holder which operates as a high gain transimpedance preamplifier. Results of microscopy and spectroscopy using a Au/n-GaAs Schottky device demonstrate the effectiveness of our design.

We present nanometer-scale resolution, ballistic electron emission microscopy (BEEM) studies of Au/octanedithiol/n-GaAs (001) diodes. The presence of the molecule dramatically increases the BEEM threshold voltage and displays an unusual transport signature as compared to reference Au/GaAs diodes. Furthermore, BEEM images indicate laterally inhomogeneous interfacial structure. We present calculations that address the role of the molecular layer at the interface. Our results indicate that spatially resolved measurements add new insight to studies using conventional spatial-averaging techniques.

We characterize our InAs/AlSb double tunnel barrier heterostructure as the base electrode with the well thickness of 12 nm and symmetric barrier thickness of 2 nm by ballistic electron emission microscopy/spectroscopy using the top InAs layer of heterostructures. We present the influence of the InAs base layer thickness (3 nm, 10 nm) and the influence of the surface passivation on results of spectroscopic measurement. The mean measured barrier height was 1.11 (±0.03) eV independent of the thickness of the InAs base electrode. The mean measured height of barriers in the case of the passivated InAs base layer was found to be lower and equal to 1.059 (±0.03) eV. We also detect thresholds in spectroscopic characteristics which are in accordance with the energy of the second resonant level in the well, and with energies that are combinations of thresholds for electron–hole pair creation processes in InAs and the energy of the second resonant level in the well. A ballistic electron emission microscopy picture at a constant voltage of 1.25 V is presented.

Semiconductor heterostructures, such as double-barrier resonant tunnelling diodes and superlattices, are nowadays used for many applications. One very versatile and powerful method to study electronic transport in heterostructures is hot electron spectroscopy. Hot electron spectroscopy can be carried out in two complementary versions: device-based techniques usually employ so-called hot electron transistors (HETs), while ballistic electron emission microscopy (BEEM) uses a scanning tunnelling microscope (STM) as the source of ballistic electrons.In this review, spectroscopic results obtained by these two methods are compared and discussed. It is shown that BEEM results are strongly influenced by electron refraction effects, while the behaviour of HET devices is dominated by inelastic scattering effects in the base and drift region of the device. Thus, STM-based BEEM/S and HET-based spectroscopy are genuinely complementary methods, which yield supplementary results.

High-temperature-processing-induced “double-stacking fault” cubic inclusions in 4H-SiC were studied with ballistic electron emission microscopy (BEEM). Large BEEM current and a ∼0.53 eV local reduction in the Schottky barrier height (SBH) were observed where the inclusions intersect a Pt interface, confirming the quantum-well nature of the inclusions and providing nanometer scale information about local electronic behavior. Measured spatial variations in the BEEM current are related to the inclusion orientation and local surface step structure. An observation of an anomalously low SBH is discussed, suggesting the existence of a triple- or quadruple-stacking fault inclusion.

A ballistic electron emission microscopy facility has been used to investigate hot electron transport through Au/M/Au and Au/M thin films (M = Fe, Co) grown on GaAs(100) substrates. The hot electron attenuation through the Au/Fe/Au trilayer roughly exhibited an exponential relationship with Fe interlayer thickness. Two values of Fe thickness (0.4 and 0.85 nm) were used to compare the differences between Fe embedded at the centre of the Au layer and Fe at the metal–semiconductor interface. For the thicker Fe layer, there is a large difference in terms of the transmitted ballistic electrons between the two structures, with the 'at-interface' structure exhibiting substantially increased transmission. This difference was not found in the Au/Co system with comparable Co thickness. The results suggest that the behaviour of transmitted hot electrons is dominated by the formation of the continuous metal layers with strong scattering at the metal–metal interfaces.

Ballistic electron emission microscopy (BEEM) is a three terminal extension of scanning tunneling microscopy and yields topographic and spectroscopic information on high-energy electron transport in semiconductors at nm-resolution. In BEEM on GaAs–AlGaAs double barrier resonant tunneling diodes (DBRTDs) ballistic electrons which tunnel through a resonant state inside the DBRTD result in a characteristic linear behavior in the BEEM spectrum. On DBRTDs nanostructured into narrow quantum wires, however, this tunneling is quenched for electron energies below the AlGaAs barrier heights. This quenching of the ballistic current can be explained in terms of a transfer Hamiltonian formalism applied to tunneling processes between electron systems of different dimensionality. We measured BEEM spectra on InAs self-assembled quantum dots (SAQDs) for positions on the dots and for “off-dot” regions on the so-called InAs wetting layer. From these data, we determined the local InAs–GaAs band offsets on the dots and on the wetting layer and investigated the temperature dependence of the InAs–GaAs barrier height.

We probe electron transport across the Au/organic interface based on oriented thin films of the high-performance n-type perylene diimide semiconductor PDI8-CN2. To this purpose, we prepared organic-on-inorganic Schottky diodes, with Au directly evaporated onto PDI8-CN2 grown on n-Si. Temperature-dependent current–voltage characteristics and complementary ballistic electron emission microscopy studies reveal that rectification at the Au/PDI8-CN2 interface is controlled by a spatially inhomogeneous injection barrier, that varies on a length scale of tens of nanometers according to a Gaussian distribution with mean value ∼0.94 eV and standard deviation ∼100 meV. The former gradually shifts to ∼1.04 eV on increasing PDI8-CN2 thickness from 5 nm to 50 nm. Experimental evidences and general arguments further allow to establish the energetics at the Au/PDI8-CN2 interface. Our work indicates injection-limited current flow in PDI8-CN2-based devices with evaporated Au electrodes. Furthermore, it suggests chemical reactivity of PDI8-CN2 with both Au and Si, driven by the lateral isocyano groups.

We have made finite element calculations of the expected potential profile around negatively charged threading dislocations (TDs) close to a metal–semiconductor interface, using a Pt contact on n-type GaN as a specific case. The potential was calculated as a function of the assumed linear density and energy level of TD-related acceptors. Our model shows good agreement with the model of Read [W. T. Read, Philos. Mag. 45, 775 (1954); 46, 111 (1954)] for an infinite dislocation, far from any interface. Assuming 1 acceptor/c-axis lattice spacing (c=0.52 nm), we found for our near-surface modeling that acceptors levels deeper than 1.3 eV below the conduction band minimum (CBM) should be charged all the way to the Pt/GaN interface. This should produce a significant local increase in the potential barrier and at the Pt/GaN interface and should be observable by ballistic electron emission microscopy (BEEM). In fact recent BEEM measurements by Im et al. on molecular beam epitaxy-grown GaN films [Phys. Rev. Lett. 8...

Ballistic electron emission microscopy (BEEM) and non-contact atomic force microscopy (NC-AFM) are used to characterize SiO2 and Al2O3 layers grown on Si(1 0 0). The effective conduction band mass and its energy dispersion in SiO2 and an offset between Al2O3 and Si conduction bands of 2.78 eV were obtained with BEEM. NC-AFM was used to image electrons, and in some instances holes, trapped in the oxide layers near the surface and in the bulk of the oxide. Modeling of the tip–surface interaction supports the interpretation of image features arising from a single electron occupying a trap. The polarity of the trapped charge was deduced from Kelvin (potential difference) images that were simultaneously recorded with the topographic images.

Hot electron generation was measured under the impact of energetic Ar and Rb ions on Ag thin film Schottky diodes. The energy- and angular-dependence of the current measured at the backside of the device due to ion bombardment at the frontside is reported. A sharp upturn in the energy dependent yield is consistent with a kinetic emission model for electronic excitations utilizing the device Schottky barrier as determined from current–voltage characteristics. Backside currents measured for ion incident angles of ±30° are strongly peaked about 0° (normal incidence) and resemble results seen in other contexts, e.g., ballistic electron emission microscopy. Accounting for the increased transport distance for excited charges at non-normal incidence, the angular results are consistent with the accepted mean free path for electrons in Ag films.

The ability to detect localized silicide formation at a buried metal semiconductor Schottky interface is demonstrated via nanoscale measurements of the electrostatic barrier. This is accomplished by mapping the Schottky barrier height of the Cr/Si(001) interface by ballistic electron emission microscopy (BEEM). Monte-Carlo modeling is employed to simulate the distributions of barrier heights that include scattering of the electrons that traverse the metal layer and a distribution of electrostatic barriers at the interface. The best agreement between the model and the data is achieved when specifying two barrier heights less than 60 meV from one another instead of a singular barrier. This provides strong evidence that localized silicide formation occurs that would be difficult to observe in averaged BEEM spectra or conventional current voltage measurements.

A comparative study between n-GaAs/Au contacts, formed by electrochemical deposition or by vacuum evaporation, is presented. The main parameter, the barrier height ?B, was determined using three methods, i.e.?classical current-voltage and capacitance-voltage measurements as well as STM-based ballistic electron emission microscopy (BEEM). The latter method allowed us to determine the distribution of ?B over the contact area on a nanometre scale and showed that the electrochemically made contacts are inhomogeneous. The main result, confirmed by the three methods, was that ?B was higher for the electrochemically deposited contacts than for the evaporated ones. This higher value is attributed to O- groups, present at the interface during the electrochemical metallization, and forming interfacial dipoles with the Au, leading to an increase of the barrier.

Ballistic Electron Emission Microscopy (BEEM) has been shown to be a powerful tool for nanometer-scale characterization of the spatial and electronic properties of semiconductor structures. In this article, we will discuss general aspects of BEEM experiment and theory in true ballistic and quasi-ballistic hot carrier transport. We will review the current state and recent progress in the use of the BEEM imaging and spectroscopy to study metal-semiconductor and metal-insulator-semiconductor interfaces, buried semiconductor heterojunctions and novel quantum objects. Various theoretical BEEM models are discussed, and their ability to describe BEEM experiments is examined. Special attention is drawn to the role of the electron scattering in the metal base layer, at the metal–semiconductor interface and in the semiconductor heterostructure on BEEM spectra.

Using a Keldysh Green's function formalism we have theoretically studied ballistic electron emission microscopy BEEM currents through Au/Si(1 0 0) and Au/Si(1 1 1) structures as a function of Au thickness. Our analysis shows that for thin films, BEEM current is greater for Si(1 0 0) than for Si(1 1 1) substrates; however, in the case of thick films (more than 15 nm) the BEEM current associated with the Si(1 1 1) orientation is greater, in agreement with recent experimental data. This behaviour is due to the change in the symmetry of the k -space current distribution after the electrons propagate through the Au lattice, changing from a sixfold symmetry (which favours the matching with Si(1 0 0) available states) to a threefold one as thickness increases. Moreover, we have analysed how the relative alignment of the metal and the semiconductor affects the final BEEM current. All these results show that taking into account the band structure of the metallic layer is essential for a detailed understanding of the transport process.

In this article, ballistic electron emission microscopy (BEEM) induced modifications on Au/Si and Au/SiO2/Si contacts are presented. BEEM current can be locally enhanced or reduced in a controlled manner. These observations are attributed to tip induced modifications on the gold surface. According to Au thickness, x-ray reflectivity experiments show different surface evolutions correlated to the size variations of the modifications introduced as a function of time.

In this work, GaAs-AlGaAs double barrier res- onant tunneling diodes (RTDs) are investigated by ballistic electron emission microscopy (BEEM). RTDs grown directly below the sample surface exhibit characteristic steplike fea- tures in the BEEM spectrum, whereas for buried RTDs, a lin- ear spectrum is observed. Moreover, the BEEM spectra of sub-surface RTDs show Shubnikov-de Haas-like oscillations in magnetic fields. To investigate the origin of these effects, the BEEM spec- tra were calculated using a scattering formalism within the framework of a semi-empirical tight binding method. As a main result we found that, independent of the applied bias, only electrons within a narrow kdistribution are transferred resonantly through the RTD. Hence, a kfilter is established for ballistic electrons close to k� = 0. The calculated filter width is consistent with the magnetic field data.

Au/Si and PtSi/Si Schottky contacts were prepared on n-Si(100) substrates which had been previously subjected to an Ar ion bombardment with well defined energies ranging from 100 eV to 1.5 keV. Samples were investigated by current-voltage (I-V) measurements, ballistic electron emission microscopy (BEEM) and deep-level transient spectroscopy (DLTS). Both I-V and BEEM results show that the effective Schottky barrier height (SBH) decreases with increasing Ar ion energy. The lowering of the barrier height is attributed to the bombardment-induced donor-like defects with relatively high densities near the silicon surface. DLTS spectra show the presence of defect levels both in the form of discrete energy levels and as a continuum of states. The oxygen-vacancy pair located at 0.16 eV below the conduction band is the dominant defect for the samples bombarded by 100 and 200 eV Ar ions and its peak signal intensity is similar for the two energies. For 300 eV or higher-energy ion-bombarded samples, other defects develop and become dominant. Their peak signal intensities increase monotonically with Ar ion energy. The variation of the DLTS spectra is in qualitative agreement with the tendency of effective SBH lowering for increasing energy of the bombarding Ar ions.