Semiconductors In Electric Fields Research Articles

On the possibility of fundamentally new, profile photoelectric effects 
 in semiconductors

Theoretically predicted that under specific nonuniform profiles of carrier photogeneration density along electric field in semiconductors three unexpected effects can occur. Those are self-amplification and self-quenching of charge carriers photogeneration rate density and selfinversion of its sign. The effects are due to the local photoinduced space charge. The shapes of profiles depend on semiconductor parameters, electric field strength in semiconductor and temperature. Examples of specific profiles for all three types of effects are given.

On the Possibility of a Significant Increase in Semiconductors Photosensitivity Spatial Profiling Flux of Radiation.

Abstract Theory-based, three new unknown photoelectric effects can be occurred in semiconductors under inhomogeneous optical illumination with specific profile shapes along electric field in semiconductor: self-amplification, self-quenching and sign self-inversion of photogeneration rate of mobile charge carriers. The general shapes of corresponding illumination profiles are calculated. The occurring effects cause by local photoexcited space charge (PSC). It is shown that profile shapes depend on parameters of semiconductor, dark electric field strength and temperature. Also, we determine general shapes of “neutral” profiles when local PSC although exists but does not affect the result of interaction of optical radiation with a semiconductor. In other words, calculations with such “neutral” profiles lead to the same result as with using quasi-neutrality approximation, which does not account PSC. The shape of “neutral” profile depends only on dark electric field strength, temperature and sample size along the electric field. Embodiments for all types of profiles are given. The results can be used in practice, first, to increasing significantly photoelectric response of semiconductor detectors of optical radiation.

Investigation of velocity overshoot behavior in p-i-n GaAs semiconductor: The contribution of internal electric field

In this work, we present the investigation of the velocity overshoot behavior in p-i-n GaAs semiconductor based on the ensemble Monte Carlo simulations. Our simulations with high-resolution of time and spatial show that the velocity overshoot effect is originated from internal electric field caused by the difference of carrier density. And this effect is dependent not only on the carrier density but also on temperature. Furthermore, we have observed the velocity relaxation effect which was not recognized before because the external electric field is too high comparing to the internal electric field in semiconductor. We point out that the velocity relaxation can be seen as a damping oscillation in which the damping velocity depends strongly on carrier density but not temperature.

Direct comparison of off-axis holography and differential phase contrast for the mapping of electric fields in semiconductors by transmission electron microscopy.

To provide a direct comparison, off-axis holography and differential phase contrast have been performed using the same microscope on the same specimens for the measurement of active dopants and piezoelectric fields. The sensitivity and spatial resolution of the two techniques have been assessed through the study of a simple silicon p-n junction observed at different bias voltages applied in-situ. For an evaluation of limitations and artefacts of the methods in more complicated systems a silicon pMOS device and an InGaN/GaN superlattice with 2.2-nm In0.15Ga0.85N quantum wells is investigated. We demonstrate the effects of dynamical scattering on the electric field measurements in the presence of local strain-induced sample tilts and its dependence on parameters like the convergence angle.

Poole-Frenkel effect in chalcogenide semiconductors with various crystalline structures

The results of investigation of electrical conductivity of a large group of chalcogenide semiconductors having the layered, cubic, and orthorhombic structures in strong electric fields up to 105 V/cm are presented. The revealed increase in electrical conductivity σ in strong electric fields has been explained by the Frenkel thermionic ionization. This has made it possible, along with other parameters (for example, activation energy and trap concentration, charge-carrier mean free path, permittivity), to evaluate the concentration and mobility of charge carriers in semiconductors under study. It has been shown that in strong electric fields in semiconductors, when the thermionic ionization of the traps occurs, their permittivity ɛ, which is caused by the electron polarization, is determined by the simple formula ɛ = n 2, where n is the refractive index of light.

Impact of Quantization Energy and Gate Leakage in Bilayer Tunneling Transistors

The effect of quantum mechanical confinement in recently proposed thin-body double-gate electron-hole bilayer tunneling transistors is examined. In such devices, a vertical electric field, which is produced by oppositely biased double gates, induces vertical band-to-band tunneling across the intrinsic semiconductor channel. It is found that reducing body thickness in order to increase tunneling probability, i.e., source-drain current drive, considerably increases confinement energy, requiring a large gate and semiconductor electric field, and therefore voltage, to reach electron and hole eigenstate alignment. Furthermore, large electric fields across the gate dielectrics are expected to cause substantial gate leakage current. Design limits based on this analysis are discussed.

1/f NOISE COMPONENT CONDITIONED BY BUILT-IN ELECTRIC FIELD IN SEMICONDUCTORS

The influence of the built-in electric field on the low-frequency current fluctuations in n-type non-degenerate homogeneous semiconductors at presence of constant external electric and magnetic fields is examined. The problem is considered by means of Langevin-type Boltzmann transport equations for the electron and phonon systems at domination of electron–acoustic phonon scatterings. For the first time, it is shown that within the context of the introduced problem, the spectral density of the current noise contains 1/f component specified by the built-in electric field. By form it is similar to the empiric Hooge formula. On the basis of the computations, a model explaining the physical mechanism of the origin of the additional component of 1/f noise, conditioned by the presence of the built-in electric field in semiconductor, is proposed. For the Hooge parameter, a comparison with the experimental data of generally observed 1/f noise for Si samples is carried out. The comparison shows that at some "favorable" conditions, the level of this new component of the 1/f noise can reach the level of the generally observed 1/f noise.

Ultrafast Control of Hole Spin by Electric Field in Semiconductors

Ultrafast and coherent transitions induced by electric field between spin states of the valence band in semiconductors are considered. It is shown that using optimized femtosecond electric fields one can, in principle, control a selected component of the hole spin. The feasibility of hole spin switching is illustrated using the well-known Luttinger-Kohn Hamiltonian for valence bands of tetrahedral and zinc-blende semiconductors. The presented results may be useful in the development of the ultrafast semiconductor spintronics.

Theory of fluctuations around a nonequilibrium state maintained by interband optical and driving electric field in semiconductors

Theory of fluctuations around a nonequilibrium state slowly varying in space and time in two-band semiconductors is developed. The derivation of kinetic equations for fluctuations within the framework of the Keldysh formalism is given. The system is supposed to be under the action of a classic optical and external driving electric field, which can displace the system substantially from equilibrium with a thermal bath, while the carriers can interact also with phonons, with one another via the Coulomb potential, and with the thermal photons causing interband recombination and generation. Matrix of correlation functions for Langevin random forces is obtained. It is shown that in the nonequilibrium state there is an extra correlation contribution of Coulomb and phonon scattering to the correlation functions of the Langevin forces.

Franz–Keldysh oscillations in modulation spectroscopy

In the presence of an electric field, the dielectric constant of a semiconductor exhibits Franz–Keldysh oscillations (FKO), which can be detected by modulated reflectance. Although it could be a powerful and simple method to study the electric fields/charge distributions in various semiconductor structures, in the past it has proven to be more complex. This is due to nonuniform fields and impurity induced broadening, which reduce the number of detectible Franz–Keldysh oscillations, and introduce uncertainties into the measurement. In 1989, a new structure, surface–undoped–doped (s-i-n+/s-i-p+) was developed, which allows the observation of a large number of FKOs and, hence, permitting accurate determination of electric fields. We present a review of the work on measuring electric fields in semiconductors with a particular emphasis on microstructures using the specialized layer sequence. We first discuss the general theory of modulation techniques dwelling on the approximations and their relevance. The case of uniform field, obtained with this specialized structure as well as that of the nonuniform field, are addressed. The various experimental techniques are also briefly reviewed. We then summarize the various experimental results obtained in the last few years using these special structures and FKOs and find that, even in this short period, good use has been made of the technique and the structure. This is followed by a brief review of the work on nonuniform fields. In this case, the work on actual device structures has significant technological implications. Important issues such as metallization and processing, the effects of surface treatment and thermal annealing, Schottky barrier heights of different metals, piezoelectric fields in (111) grown strained InGaAs/GaAs quantum wells, and Fermi level in low-temperature grown GaAs have been studied using this structure. This structure has also been used to study the dynamics of photomodulation, revealing the nature of the cw photoreflectance.

Coherent effects induced by static and time-dependent electric fields in semiconductors.

Coherent effects are analyzed that are induced by homogeneous electric fields in photoexcited semiconductors. Extended semiconductor Bloch equations are presented, which include the applied electric field, in addition to the many-body Coulomb contributions in the time-dependent Hartree-Fock approximation. These equations are solved for a one-dimensional tight-binding model of a semiconductor superlattice. Linear and nonlinear optical signals associated with the coherent field-induced effects are calculated. For the case of a static electric field, the influence of the Coulomb interaction, which is treated on the Hartree-Fock level for a contact potential approximation, on the Bloch oscillations, and on their counterpart in the frequency domain, the Wannier-Stark-ladder, is analyzed. For a time-dependent electric field, dynamic localization, i.e., the localization of electrons due to an oscillating electric field, is analyzed. It is predicted that the dynamic localization should be observable in semiconductor superlattices even in the presence of Coulomb interaction.

Thermoelectric power of hot carriers in the nonequilibrium-statistical-operator approach.

The thermoelectric power of charge carriers heated under a strong applied electric field in semiconductors is obtained by use of the nonequilibrium-statistical-operator (NSO) method. The balance equations are derived in terms of the NSO density matrix and the force-force correlation functions which can easily be calculated for a system with electron-impurity and electron-phonon interactions. A numerical study has been performed for hole-doped Ge. It is shown that the hot-electron thermoelectric power is sensitively affected by the applied electric field and that its sign is reversed at higher electric fields.

Defect Chemistry: Composition, Transport, and Reactions in the Solid State; Part II: Kinetics

AbstractWithin the last few decades—though with its beginnings traceable to as early as 60 years ago—a direction of research has developed almost unnoticed by the classical chemical disciplines, such that one can now recognize a chemistry within the solid state that is analogous to the long‐familiar chemistry in the liquid state. It arises from those departures from the ideal structure that are thermodynamically unavoidable, the point defects, and is referred to as defect chemistry. It includes the description of ionic and electronic effects, and it considers diffusion as a special step of the overall reaction. This area of chemistry enables one to describe and treat in a unified way many apparently widely different phenomena such as ionic conduction in crystals, doping effects and p–n junctions in semiconductors, color centers in alkali metal halides, image development in photography, passivation and corrosion of metals, the kinetics of the synthesis and sintering of solid materials, the problems of rock formation during the earth's evolution, the mechanisms of gas sensors and high temperature fuel cells, the performance of photosentive electrodes, variations of the electron balance in high temperature superconductors, elementary processes of heterogeneous catalysis, nonequilibrium transitions and oscillations in semiconductors in electric fields, and many more. In such phenomena the equilibrium concentration of defects has an important double role: it not only determines the disorder and the departures from the stoichiometric composition in the equilibrium state, but also, together with the mobility as the kinetic parameter, is the key parameter concerning the rates of physical processes, which are the main subject of the present discussion. Following the account of the thermodynamic fundamentals in Part I, this second part of the review will be concerned with kinetic processes. These are essentially the equilibration processes (physical diffusion, electrical conduction, chemical diffusion, and reactions) that take place under the influence of chemical and electric driving forces. As in Part I, here again the general characteristics of defect chemistry will clearly emerge, including the coexistence of ionic and electronic charge carriers, and the importance of the spatial coordinates. The concluding section will discuss some special characteristics of nonlinear processes that are too often overlooked in solid‐state studies.

Defect Chemistry: Composition, Transport, and Reactions in the Solid State; Part I: Thermodynamics

AbstractWithin the last few decades—though its foundations were laid over 60 years ago—a direction of research has developed almost unnoticed by the classical chemical disciplines, such that one can now recognize a chemistry within the solid state that is analogous to the long‐familiar chemistry in the liquid state. It arises from those departures from the ideal structure that are thermodynamically unavoidable, the point defects, and is referred to as defect chemistry. It includes the description of ionic and electronic effects, and it considers diffusion as a special step of the overall reaction. This area of chemistry enables one to describe and treat in a unified way many widely different phenomena such as ionic conduction in crystals, doping effects and p–n junctions in semiconductors, color centers in alkali metal halides, image development in photography, passivation and corrosion of metals, the kinetics of synthesis and sintering of solid materials, problems of rock formation during the earth's evolution, the mechanisms of gas sensors and high temperature fuel cells, the performance of photosensitive electrodes, variations of the electron balance in high‐temperature superconductors, elementary processes of heterogeneous catalysis, nonequilibrium transitions and oscillations in semiconductors in electric fields, and many more. In such phenomena the equilibrium concentration of defects has an important double role: it not only determines the disorder and the departure from the Dalton composition in the equilibrium state, but also, together with the mobility as the kinetic parameter, is the key parameter concerning the rates of physicochemical processes. Accordingly, in this first part of the review the emphasis will be on the equilibrium thermodynamics of point defects, whereas the second part will be specifically concerned with the kinetic aspects. Both parts will emphasize the fact that the defect chemistry of solids, as well as being the counterpart of solution chemistry in the liquid state, also provides a unifying approach in which electronic and ionic charge carriers are treated by analogous methods, both in the bulk and in boundary layers, and allows diffusion to be incorporated naturally into the overall kinetics of reactions as an elementary chemical process.

The Odd Voigt Effect under a Strong Electric Field in Semiconductors

AbstractThe high‐frequency conductivity tensor σik(ω) in the linear approximation of magnetic field H and in quadratic approximation of external de electric field is derived by solving the Boltzmann equation. The magneto‐optical phenomena in the Voigt configuration (when the probe electromagnetic wave propagates across the magnetic field) are investigated. It is shown that birefringence and dichroism have a component that is odd (linear) in the magnetic field and predominates over the even effect in weak magnetic field.

Quantum effects on electron-phonon interaction under high electric field in semiconductors

Quantum effects on the electron-phonon interaction under high electric fields are investigated by a fully quantum mechanical method in the real space representation, in which electric fields are included in the unperturbed Hamiltonian and the electron-phonon interactions are incorporated through the perturbation scheme. The intracollisional field effect and the interference effect associated with the wave character of electron under high electric fields are investigated. It is explicitly shown that the intracollisional field effect becomes significant when the electric field is above tens of kV cm-1 and that the interference effect is reduced as the electric field becomes greater.

Terahertz Beams: Generation and Spectroscopy

ABSTRACTTeraHertz beams of ultrafast pulses of far infrared (λ=40–1000μm, v = 0.3x1012− 7.5×1012Hz) radiation generated via the induced dipole of photogenerated charge within a strong electric field in semiconductors are an emerging spectroscopic technique which incorporates ultrafast optical pulse generation, optoelectronics, and far infrared techniques. Recent results obtained using the trap enhanced field (TEF)[1] effect in the generation of THz beams demonstrate the extended frequency range of these sources and show their importance to time resolved infrared spectroscopy.The generation of collimated THz radiation within semi-insulating materials is dramatically improved by the extremely large field enhancement near the anode of an electrically biased metal/semi-insulator/metal structure. Our experimental results for semiinsulating GaAs establish an operational regime in which the applied potential is confined to a small region near the anode resulting from a space charge region which exists due to a dramatic change in the number of ionized EL2 traps. The effect, contrary to that observed in trap free or doped materials, is enhanced by optical injection of carriers near the anode, and can be exploited for the efficient generation of ultrafast THz radiation.Spectroscopy using THz beams allows both the static and dynamic properties, including refractive index, absorption, and photoconductivity, of materials and structures to be accurately measured. The energy range and time resolution of freely propagating subpsec THz pulses have not been previously available.

Nonequilibrium electrons and phonons in ?massive? semiconductors in electric fields

A new approach is proposed for study of electron and phonon heating by a constant electric current. Phonon heating conditions and their effect on electron heating are established for thick specimens.

A quantum description of drift velocity overshoot at high electric fields in semiconductors

A quantum description of transient charge transport in semiconductors is presented. In particular, we discuss the drift velocity overshoot in GaAs. The paper is intended to show how typical quantum features, such as intracollisional field effect and multiple collisions tend to modify the transient behavior of the system as predicted by semiclassical transport. This analysis has been performed by means of a quantum Monte Carlo procedure which takes into account the GaAs band structure through a many-valley model. The results of the quantum simulation, as regards drift velocity and upper valley population, have been compared with those of the classical theory and this comparison shows that in the case of GaAs quantum features are not relevant. For a better understanding, a semiconductor model, characterized by a very strong electron-phonon coupling constant, has been considered where quantum effects are appreciable and from this analysis it is possible to identify physical systems for which a full quantum treatment is required.

High-resolution X-ray studies of microstructural changes associated with conduction at high electric fields in semiconductors and insulators

High-resolution X-ray studies of microstructural changes associated with conduction at high electric fields in semiconductors and insulators