Ballistic Electron Injection Research Articles

Ballistic Injection Terahertz Plasma Instability in Graphene n+–i–n–n+ Field‐Effect Transistors and Lateral Diodes

The operation of the graphene n+–i–n–n+ field‐effect transistors (GFETs) and lateral diodes (GLDs) with the injection of ballistic electrons into the n‐region is analyzed. The momentum transfer of the injected ballistic electrons can lead to an effective Coulomb drag of the quasiequilibrium electrons in the n‐region and the plasma instability in the GFETs and GLDs. The instability enables the generation of terahertz radiation. The obtained results can be used for the optimization of the structures under consideration for different devices, in particular, terahertz emitters.

Coulomb Drag by Injected Ballistic Carriers in Graphene n+−i−n−n+ Structures: Doping and Temperature Effects

The Coulomb carrier drag effect in lateral −i−n− graphene diodes and field‐effect transistors with the injection of ballistic electrons into the n‐region are evaluated. Calculating the drag factor determining the amplification of the injected current, its dependence on the structural parameters, carrier Fermi energy in the n‐region, and temperature is found. As demonstrated, the drag factor exhibits a maximum in certain values of the Fermi energy (i.e., the gate voltage and density of the remote donors) and the temperature. The parameter determining the shape of the current–voltage characteristics (monotonous or S shaped) is also calculated. The obtained results can be used for the optimization of the structures under consideration for different devices, in particular, voltage‐ and current‐driven switches, frequency multipliers, and terahertz emitters.

Two-dimensional Rutherford-like scattering in ballistic nanodevices

Ballistic injection in a nanodevice is a complex process where electrons can either be transmitted or reflected, thereby introducing deviations from the otherwise quantized conductance. In this context, quantum rings (QRs) appear as model geometries: in a semiclassical view, most electrons bounce against the central QR antidot, which strongly reduces injection efficiency. Thanks to an analogy with Rutherford scattering, we show that a local partial depletion of the QR close to the edge of the antidot can counter-intuitively ease ballistic electron injection. On the contrary, local charge accumulation can focus the semi-classical trajectories on the hard-wall potential and strongly enhance reflection back to the lead. Scanning gate experiments on a ballistic QR, and simulations of the conductance of the same device are consistent, and agree to show that the effect is directly proportional to the ratio between the strength of the perturbation and the Fermi energy. Our observation surprisingly fits the simple Rutherford formalism in two-dimensions in the classical limit.

Low-Temperature Deposition of Thin Si, Ge, and SiGe Films Using Reducing Activity of Ballistic Hot Electrons

It is shown that a wet process for thin Si and Ge films deposition based on the ballistic electron injection into solutions is available for SiGe. A nanocrystalline silicon (nc-Si) diode is composed of a thin Au (10 nm)/Ti (1 nm) film surface electrode, nc-Si layer (~1 µm), n+-Si substrate, and back contact. The electrochemical effect of ballistic hot electrons was confirmed by cyclic voltammetry analyses. Electrons are emitted from the nc-Si device on which a very small amount of SiCl4+GeCl4 solutions is dripped. After the emitter operation, thin SiGe films are deposited on the emitting surface with neither byproducts nor contaminations as in the case of thin Si and Ge films deposition. Based on the structural and compositional characterizations of deposited SiGe films, the specific features of this reduction-induced deposition mode are discussed in comparison with the conventional processes.

Liquid-Phase Deposition of Thin Si and Ge Films Based on Ballistic Electro-reduction

An alternative wet process for depositing thin Si and Ge films is presented based on the ballistic electron injection into solutions. A nanocrystalline silicon (nc-Si) diode, composed of a thin Au (10 nm), nc-Si layer (~1 µm), polycrystalline silicon, and n+-Si substrate, operates as a surface-emitting active cold cathode in solutions. When driven alone in SiCl4 and GeCl4 solutions without using any counter electrodes, quasi-ballistic electrons generated in the nc-Si layer and ejected from the outer surface directly reduce Si and Ge ions followed by the deposition of thin amorphous Si4+ and Ge4+ films on the emitting surface with neither byproducts nor contaminations. Based on the structural and compositional characterizations of deposited Si and Ge films, the specific features of this deposition mode are discussed in comparison with the conventional dry process.

Investigation of energy levels of Er-impurity centers in Si by the method of ballistic electron emission spectroscopy

The method of ballistic electron emission spectroscopy is used for the first time to study the energy spectrum of Er-impurity complexes in Si. The features are observed in the ballistic electron spectra of mesa diodes based on p+-n+ Si structures with a thin (∼30 nm) p+-Si:Er surface layer in the region of ballistic-electron energies eVt lower than the conduction-band-edge energy Ec in this layer. They are associated with the tunnel injection of ballistic electrons from the probe of the scanning tunnel microscope to the deep donor levels of the Er-impurity complexes in the p+-Si:Er layer with subsequent thermal excitation into the conduction band and the diffusion to the p+-n+ junction and the direct tunneling in it. To verify this assumption, the ballistic-electron transport was simulated in the system of the Pt probe, native-oxide layer SiO2-p+-Si:Er-n+, and Si substrate. By approximating the experimental ballistic-electron spectra with the modeling spectra, the ground-state energy of the Er complex in Si was determined: Ed ≈ Ec − 0.27 eV. The indicated value is consistent with the data published previously and obtained from the measurements of the temperature dependence of the free-carrier concentration in Si:Er layers.

Micro- and nanotopographies for photoelectrochemical energy conversion. II: Photoelectrocatalysis – Classical and advanced systems

The present trends on water photolysis are shortly reviewed. For application in monolithically integrated structures, photoelectrocatalytically active half cell developments with p-Si are described. Using the concept of nanoemitter minority carrier harvesting, it is shown that the introduction of traces of noble metal catalysts that allow collection of light-induced carriers does not result in cost or scarcity limitations. The issue of charge transfer through an interfacial oxide and ballistic electron injection into the electrolyte vs. thermalization is discussed. The experimental data shows that the nanoemitter system can sustain the high current densities resulting from injected light-induced excess carriers from the semiconductor at low overvoltages. Limitations of planar systems with Si are discussed and possible improvements are outlined. First tests of Si rod-like microstructures are presented and the influence of localized surface plasmon excitation on light-induced H 2 evolution with p-Si is investigated.

Counter-Electrode-Free Thin Cu Film Deposition Based on Ballistic Electron Injection into CuSO4Solution from Nanosilicon Emitter

Counter-Electrode-Free Thin Cu Film Deposition Based on Ballistic Electron Injection into CuSO₄Solution from Nanosilicon Emitter

Counter-Electrode-Free Thin Cu Film Deposition Based on Ballistic Electron Injection into CuSO4 Solution from Nanosilicon Emitter

It is shown that a nanocrystalline silicon (nc-Si) ballistic electron emitter acts as an active electrode in a metal–salt solution (such as CuSO4 solution). The nc-Si emitter is composed of a thin Au film (10 nm thick), anodized polycrystalline layer (1 µm thick), and single-crystalline n+-Si substrate. In accordance with the results of an analysis by cyclic-voltammogram measurements under the standard three-electrode configuration, the electron injection effect into the solution is clearly observed at a potential within the electrochemical window where no electrolytic reactions appear. When the nc-Si emitter is driven alone in a CuSO4 solution without using any counter electrodes, a polycrystalline thin Cu film is uniformly formed on the emitting surface. This is presumably due to the preferential reduction of Cu2+ ions at the interface by injected energetic electrons. The observed deposition mode is different from both the conventional electroplating and electroless plating. This technique is an alternative low-temperature wet process that will be applicable to the deposition of various thin metal films.

An analytical model for steady-state currents in conjugated systems

The ‘source-and-sink-potential’ approach is used to treat the steady-state currents created by injection of ballistic electrons via external contacts into unsaturated π systems. An analytical expression is derived, within the tight-binding approximation, for the molecular transmission as a function of energy, which is cast in terms of four characteristic polynomials: those of the molecular graph and three vertex-deleted sub-graphs. The dependence of transmission on both the molecular skeleton and its mode of connection is thereby made explicit.

Characteristics of nanosilicon ballistic cold cathode in aqueous solutions as an active electrode

The effect of ballistic electron injection into aqueous solutions has been studied by nanocrystalline silicon (nc-Si) planar cold cathode. The present article shows that the nc-Si ballistic emitter operates in both pure water and a dilute H2SO4 solution, and that hydrogen gas is generated with no by-product like oxygen. The hydrogen evolution rate in H2SO4 solution was higher than that in water as expected. In water, the pH value shows a significant increase toward the alkaline side during the device operation without using any counterelectrode. These results support the model that energetic electrons emitted from the device into solutions directly reduce H+ ions at the interface. The ballistic emitter is useful in solutions not only for hydrogen generation but also for control of pH level and related electrochemical properties.

Room Temperature Operation of an In-Plane Half-Adder Based on Ballistic Y–Junctions

We have realized an in-plane half-adder (HA) structure based on monolithically interconnected GaAs-AlGaAs Y-branched nanojunctions. A self-switching effect of the junction from an internal gating regime to a regime dominated by the ballistic injection of electrons from different terminals is observed at room temperature and exploited to demonstrate HA operation.

Ballistic electron emission luminescence

We describe the design, fabrication, and operation of a GaAs-based heterostructure device which emits band gap luminescence from solid-state tunnel-junction ballistic injection of electrons with sub-bandgap energy. We find that, due to energy conservation requirements, a collector bias exceeding a threshold determined by the Schottky barrier height and sample band gap energy must be applied for luminescence emission. The consequences of these results for a hybrid scanning-probe microscopy and spectroscopy combining both ballistic electron emission microscopy and scanning tunneling luminescence are emphasized.

Ballistic Electrons in Ferromagnet/Semiconductor Hybrid Structures: From Nanomagnetometry to Spin Injection

We review our recent experimental and theoretical studies on ferromagnet/semiconductor hybrid structures and discuss the role of ballistic electrons in such systems. We focus in particular on two peculiar features: first,ballistic electrons in semiconductors are shown to be in particular sensitive to local details of an inhomogeneous stray field. We argue that this can preferentially be used for nanomagnetometry. Second, we show theoretically that, in case of the injection of ballistic electrons from a metallic ferromagnet into a semiconductor, a spin-dependent interface resistance arises due to band-structure mismatch that causes spin filtering at the interface. Recent band-structure calculations suggest that for an epitaxial interface a nearly 100% spin-polarized current might be generated in a spin-injection experiment.

Ballistic and tunneling GaAs static induction transistors: nano-devices for THz electronics

GaAs static induction transistors (SIT) with 10-nm scale channel and with a 100-nm channel were fabricated with molecular layer epitaxy (MLE). Area-selective epitaxy of GaAs/AlGaAs/GaAs was used for the gate. Temperature dependence of current-voltage (I-V) characteristics of the 100-nm SIT indicates ballistic injection of electrons. In the 10-nm scale SIT, electrons are transported ballistically in the drain-side electric field. Direct tunneling is responsible for the transport through the potential barrier. It is indicated by the temperature dependence and by the electroluminescence spectrum. Electron transport in the 10-nm scale SIT is nearly scattering-free. The plausible estimation of the electron transit time is 2/spl middot/10/sup -14/ s; the worst case estimation based on saturated drift velocity gives 1/spl middot/10/sup -13/ s. It makes the ISITs suitable for THz applications. Multiple area-selective MLE GaAs regrowth was used as a tool for automatic definition of the channel length.

The Role of Ballistic Electron Emission Microscopy for Characterization of Physical Phenomena in Semiconductor Alloys and Quantum Structures

The measurement of the physical properties of individual semiconductor quantum objects at a length scale corresponding to the de Broglie wavelength of electrons in most semiconductors (a few mm) is a difficult challenge. Determination of spectroscopic properties of individual quantum objects buried below the surface is particularly daunting. In this paper we will review briefly recent progress in the use of BEEM (ballistic electron emission microscopy) for the study of semiconductor alloys and novel quantum objects. We will also discuss general aspects of BEEM experiment and theory in true ballistic and quasi-ballistic hot carrier transport. Examples of the use of this technique for studying buried heterojunctions will be presented. Potential modifications of the technique for imaging the optical emission under conditions of ballistic electron injection will also be discussed.

THE ROLE OF BALLISTIC ELECTRON EMISSION MICROSCOPY FOR CHARACTERIZATION OF PHYSICAL PHENOMENA IN SEMICONDUCTOR ALLOYS AND QUANTUM STRUCTURES

The measurement of the physical properties of individual semiconductor quantum objects at a length scale corresponding to the de Broglie wavelength of electrons in most semiconductors (a few mm) is a difficult challenge. Determination of spectroscopic properties of individual quantum objects buried below the surface is particularly daunting. In this paper we will review briefly recent progress in the use of BEEM (ballistic electron emission microscopy) for the study of semiconductor alloys and novel quantum objects. We will also discuss general aspects of BEEM experiment and theory in true ballistic and quasi-ballistic hot carrier transport. Examples of the use of this technique for studying buried heterojunctions will be presented. Potential modifications of the technique for imaging the optical emission under conditions of ballistic electron injection will also be discussed.

Carrier injection by static induction mechanism in MLE-grown planar-doped barrier n/sup +/-i-p/sup +/-i-n/sup +/ structures

The I-V characteristics of GaAs n/sup +/-i-p/sup +/-i-n/sup +/ diode structures grown by MLE with source-drain distances from 500 /spl Aring/ to 950 /spl Aring/ have been measured at temperatures ranging from 77 K to 423 K. The analysis of experimental results indicates that the current flows over the static-induction-controlled potential barrier. On this basis, quantitative comparison with thermionic emission theory which assumes injection of ballistic electrons are made.

Monte-Carlo study of the nonstationary transport in Si-SiGe HJBTs

The authors report a study by Monte-Carlo simulation of an npn HBT with a Si1-xGex base. The injection of ballistic electrons over an abrupt emitter-base heterojunction allowed the base transit time to decrease to 0.2 ps. However, the interest of this ballistic transport was limited by the following two-dimensional phenomena: the defocalization of the emitter current and the Kirk effect.

Reflection and refraction of ballistic electrons through different carrier concentration regions

Transmission and reflection characteristics of ballistic electrons are studied in a macroscopic four-terminal square device with a strip Schottky gate placed so as to bisect the device. Since the gate is negatively biased, a bend resistance peak at zero magnetic field, which is induced by ballistic electron injection into an opposite voltage probe, varies from positive to negative, and a magnetic focusing peak shifts to a lower field. These phenomena arise from the reflection of ballistic electrons crossing regions of different electron densities. The transmission and reflection probabilities are determined as a function of gate voltage, and are related to the change in the refractive index of ballistic electrons.