弱纵向外电场对磁化等离子体中哨声波的影响

本文以等离子体动力论为基础讨论存在纵向外电场时磁化等离子体的哨声波。由于外电场的影响,等离子体偏离平衡态。取电子稳态分布函数为局域的麦克斯韦分布,用沿无扰轨道积分方法求出系统的介电张量,并分别用介电张量的厄米部份和反厄米部份分析哨声的色散关系和增长率。对于波矢在以电场方向为轴顶角为2c锥角范围内的哨声,外电场的作用使波增长;波矢在此锥角范围之外,外电场的作用使其衰减。波的增长率随频率增高而增大,随波矢倾角增大而减小。ee时,波矢与外电场平行对应的最大增长率与等离子体密度成正比,与磁场强度成反比。文中还给出了以电离层F层作背景参数的数值计算结果。     

COHERENT RADIATION OF MILLIMETER WAVES GENERATED BY AN INTENSE ROTATING ANNULAR RELATIVISTIC ELECTRON BEAM

Properties of coherent radiation of millimeter waves generated by an intense rotating annularrelativistic electron beam(E-layer)which is from a cusp magnetic field are investigated.The linearizedVlasov-Maxwell equations are used to analyze the interaction between E-layer and resonators of themagnetron.The dispersion relation is deduced and numerical calculation is made.The results show that thefrequency of microwave radiation is ω_r(ω_r=lΩ〃 where Ω〃 is the electron relativistic cyclotron frequencyin the axial magnetic field;l is the azimuthal mode number,l=n+mN;N is the number of sideresonators,n=0,1,2,……N/2,m is any integer).The growth rate of radiation is still large enough even ifl is large.It is good for generating a millimeter wave radiation at low axial magnetic field.If the modes canbe controlled well,a tunable,high power millimeter wave device can be made.     

A NEW FORMULA FOR INDUCTANCE OF ANISOTROPIC MAGNETIC MEDIA

By solving the basic equations of magnetic field in the anisotropic magnetic mediain which the tensor μik is symmetric,an integral formula for anisotropic vector potential A isobtained.By which the characteristic formulae for self and mutual inductances are derived inscalar and tensor forms,and their transformation formula are also derived.Finally,the formulais checked by practical examples.     

Amplification of electromagnetic waves at odd harmonics of the cyclotron resonance of heavy holes with negative effective masses in semiconducting diamond

It is shown theoretically that the absorption coefficient for circularly polarized electromagnetic waves at the cyclotron resonance of heavy holes with negative effective masses in diamond in parallel electric and magnetic fields oriented along the [001] crystal axis takes negative values at the frequency of any of the n+1 harmonics (n=0,4,8, etc.) for the right (electron) polarization and at the frequency of any of the n−1 harmonics (n=4,8,12, etc.) for the left (hole) polarization. In an electric field E≈10⁴ V/cm and magnetic fields H=30–80 kOe, at lattice temperatures of 77–100 K, and for a hole concentration of (3–5)×10¹⁵ cm⁻³, the absorption coefficient for an electromagnetic wave at the third harmonic ω ₃=3ω=2.5×10¹² s⁻¹ (wavelength λ₃=0.92 mm) is as high as η ₃=(−7)–(−30) cm⁻¹. Fiz. Tekh. Poluprovodn. 32, 504–508 (April 1998)     

An effect of excitation of a transverse magnetic creeping wave when a transverse electric wave crosses the line of the coincidence of propagation constants

Transverse electromagnetic electric (TE) and transverse magnetic (TM) creeping waves on a surface with an anisotropic impedance boundary condition are considered. An asymptotic theory is developed for creeping waves. The theory is valid near the line where the attenuation parameters of two different types of waves coincide and, therefore, standard asymptotics are inapplicable. Asymptotic formulas describing physical effects that occur when a creeping wave propagates across the degeneracy line are derived. It is found that, behind the degeneracy line, a propagating TE wave excites a TM wave with a small amplitude (of order O(k ^−1/6)) and a propagating TM wave excites a TE wave.     

Electron localization in sound absorption oscillations in the quantum Hall effect regime

The absorption coefficient for surface acoustic waves in a piezoelectric insulator in contact with a GaAs/Al_0.25Ga_0.75As heterostructure (with two-dimensional electron mobility μ=1.3×10⁵ cm²/(V·s) at T=4.2 K) via a small gap has been investigated experimentally as a function of the frequency of the wave, the width of the vacuum gap, the magnetic field, and the temperature. The magnetic field and frequency dependences of the high-frequency conductivity (in the region 30–210 MHz) are calculated and analyzed. The experimental results can be explained if it assumed that there exists a fluctuation potential in which current carrier localization occurs. The absorption of the surface acoustic waves in an interaction with two-dimensional electrons localized in the energy “tails” of Landau levels is discussed. Fiz. Tekh. Poluprovodn. 31, 451–458 (April 1997)     

Parametric Instabilities of Two Kind of Millimeter Waves and Multiplication of Frequency in GaAs Semiconductors

This paper deals, at first, with the non-linear parametric effects on both space charge and electromagnetic waves in GaAs semiconductors. If an external electric field is applied, at the critical field value, the mobility changes its sign and becomes negative, as a result, non-linear instabilities of the interactions are obtained. At the optimal value of electric field, E _opt, all non-linear processes are very effectives. The second point is the multiplication of the wave frequency, which is also effective thanks to the non-linearity. This process is used for carring waves into millimeter range instead of generation process, which in this range is non-effective. The Multiplication effect is based on the using space charge waves.     

Frequency Transformation of a Whistler Wave by A Collapsing Plasma Medium in a Cavity: FDTD Solution

A whistler wave in a cavity filled with a magnetoplasma medium is strongly affected when the plasma source is switched-off. Due to such a collapse of the plasma, the whistler wave is converted to an electric- field-intensified higher frequency wave (with an order of magnitude upshift of the frequency). In principle, it is possible to transform a 2.45 GHz source radiation to 300 GHz Terahertz radiation, with significant strength of the electric field. Finite difference time domain (FDTD) technique is used to study the effect of the following parameters: the rate of collapse, spatial plasma-density profile, collision frequency as well as the switching angle.      

Excitation of Hypersound due to Coupling with Space Charge Waves of Millimeter Wave Range in Gan Films

The excitation of hypersonic waves (f = 30–200 GHz) due to coupling with amplified space charge waves of millimeter wave range in GaN films is investigated theoretically. An amplification of space charge waves due to the negative differential conductivity in GaN films placed onto a semi-infinite substrate is considered and possible spatial increments are calculated. Both diffusion-drift equations for volume electron concentration and also an approximation of two-dimensional electron gas were used jointly with the Poisson equation for the electric field. The amplified space charge waves can excite hypersonic waves in the substrate at the same frequency due to piezoeffect and deformation potential mechanisms. It is demonstrated that the piezoeffect seems very effective for resonant excitation of hypersonic waves in the case of a full mechanic contact of GaN film and a non-piezoelectic substrate.     

Hall effect in quasi-two-dimensional superlattices in nonquantizing magnetic and strong electric fields

The transverse electric field E _y arising in quasi-two-dimensional superlattices (SLs) in a strong pulling electric field E _x and a weak magnetic field oriented in a direction perpendicular to the plane of the SL (H ∥ Z) is calculated. In the case where the electronic energy spectrum is nonadditive, the field E _y includes the Hall factor and the spontaneous transverse electric field that exists without H. The field E _y is a multivalued and sign-variable function of E _x . The asymptotically stable branches of the function E _y are determined. The (kinetic) “potential,” whose minimum corresponds to a stationary state of the nonequilibrium electron gas, is used. Fiz. Tekh. Poluprovodn. 31, 916–919 (August 1997)     

Isofrequency surfaces and dependences of electromagnetic waves in infinite ferromagnetic space

Isofrequency surfaces and dependences of various (spin, nonresonant, and postresonant) electromagnetic waves that propagate in infinite ferromagnetic space under saturated magnetization are calculated. In a frequency interval of ω_H < ω < ω_⊥, the propagation of spin waves is characterized by open isofrequency dependences and the cutoff angles that depend on the frequency and material parameters. When the conditions are not satisfied, closed dependences are obtained. The properties of the isofrequency dependences that determine specific features of the reflection and diffraction divergence of waves are analyzed. The spin wave that propagates perpendicularly to the uniform magnetic field may exhibit zero angular width of the beam in the plane that is parallel to the magnetic field vector. In the same plane, the nonresonant wave with linear dispersion may have the diffraction divergence that is significantly less than that of the wave in isotropic media. In the presence of a plane interface, the reflection of the wave to the ferromagnetic material may give rise to two reflected beams.     

Absorption of a strong electromagnetic wave by electrons in a superlattice in a quantizing electric field

Intraminiband absorption of light by electrons in a quantum superlattice in a quantizing electric field is investigated theoretically taking into account the electron-phonon interaction. It is assumed that the interaction with optical dispersion-free phonons makes the main contribution to electron scattering. It is shown that the point ω=ω ₀ (ω is the light frequency, and ω ₀ is the optical phonon frequency) conditionally divides the ω dependence of the absorption into two parts: ω<ω ₀, the region of exponentially weak absorption and ω>ω ₀, the region of “strong” absorption. An electric field shifts the region of strong absorption in the red direction of the spectrum. Fiz. Tekh. Poluprovodn. 33, 1355–1358 (November 1999)     

Field Emission and Electric Discharge of Nanocrystalline Diamond Films

Nanocrystalline diamond (NCD) films were produced by microwave plasma-enhanced chemical vapor deposition (MPECVD) using gas mixtures of Ar, H₂, and CH₄. The structural properties, electron emission, and electric discharge behaviors of the NCD films varied with H₂ flow rates during MPECVD. The turn-on field for electron emission at a pressure of 2.66 × 10⁻⁴ Pa increased from 4.2 V μm⁻¹ for the NCD films that were deposited using a H₂ flow rate of 10 cm³ min⁻¹ to 7 V μm⁻¹ for films deposited at a H₂ flow rate of 20 cm³ min⁻¹. The NCD film with a low turn-on field also induced low breakdown voltages in N₂. The grain size and roughness of the NCD films may influence both the electron emission and the electric discharge behaviors of the NCD cathodes.     

Plane wave diffraction by a thin dielectric half-plane

Expressions that apply for all observation points are derived for the field produced by a plane wave incident on a thin dielectric half-plane when the electric vector of the incident wave is parallel to the edge. Away from shadow boundaries the total field comprises an edge wave and a surface wave in addition to the transmitted and reflected waves of geometrical optics. The nature of the edge wave differs from that of a perfectly conducting half-plane in that both the amplitude and phase vary with the observation angle, for a given angle of incidence.     

Photoelectric properties of n-CdS/p-InP heterojunctions

The polarization method for studying photoactive absorption is used to investigate the photoconversion processes in CdS/InP heterojunctions as a function of the orientation of the indium phosphide substrate. The results of these investigations demonstrate the sensitivity of the photoelectric processes to several factors, including the crystallographic orientation of the p-type InP substrate and the optical quality of the CdS layer. The induced photopleochroism coefficient of these heterojunctions increases proportionally to the square of the angle of incidence (P _I ∼Θ²). Such CdS/InP heterojunctions can be employed as polarization-photosensitive devices. Fiz. Tekh. Poluprovodn. 32, 72–77 (January 1998)     

Wannier-Stark states in a superlattice of InAs/GaAs quantum dots

Electron and hole emission from states of a ten-layer system of tunneling-coupled vertically correlated InAs/GaAs quantum dots (QDs) is studied experimentally by capacitance—voltage measurements and deep-level transient spectroscopy. The thickness of GaAs interlayers separating sheets of InAs QDs was ≈3 nm, as determined from transmission electron microscope images. It is found that the periodic multimo-dal DLTS spectrum of this structure exhibits a pronounced linear shift as the reverse-bias voltage U _r applied to the structure is varied. The observed behavior is a manifestation of the Wannier—Stark effect in the InAs/GaAs superlattice, where the presence of an external electric field leads to the suppression of coupling between the wave functions of electron states forming the miniband and to the appearance of a series of discrete levels called Wannier—Stark ladder states.     

The nature of electrical interaction of Schottky contacts

Electrical interaction between metal-semiconductor contacts combined in a diode matrix with a Schottky barrier manifests itself in an appreciable variation in their surface potentials and static current-volt-characteristics. The necessary condition for appearance of electrical interaction between such contacts consists in the presence of a peripheral electric field (a halo) around them; this field propagates to a fairly large distances (<30 μm). The sufficient condition is the presence of regions where the above halos overlap. It has been shown that variation in the surface potential and the current-voltage characteristics of contacts occurs under the effect of the intrinsic electric field of the contact’s periphery and also under the effect of an electric field at matrix periphery; the latter field is formed as a result of superposition of electric fields of halos which form its contacts. The degree of the corresponding effect is governed by the distance between contacts and by the total charge of the space charge regions for all contacts of the matrix: their number, sizes (diameter D _{i, j} ), concentration of doping impurities in the semiconductor N _D , and physical nature of a metal-semiconductor system with a Schottky barrier (with the barrier height φ _b ). It is established that bringing the contacts closer leads to a relative decrease in the threshold value of the “dead” zone in the forward current-voltage characteristics, an increase in the effective height of the barrier, and an insignificant increase in the nonideality factor. An increase in the total area of contacts (a total electric charge in the space charge region) in the matrix brings about an increase in the threshold value of the “dead” zone, a relative decrease in the effective barrier height, and an insignificant increase in the ideality factor.     

Ionization of impurity centers in a semiconductor quantum superlattice by nonlinear electromagnetic waves

The ionization of impurity centers in a semiconductor superlattice by nonlinear electromagnetic waves, which are the most general solution of the sine-Gordon equation and can be expressed in terms of the Jacobi elliptic functions, is investigated. The problem is solved in a quasiclassical approximation for arbitrary ratio of V (depth of the impurity energy level) and Δ (half-width of the conduction miniband). Results in agreement with those for solitary waves and sinusoidal (linear) electromagnetic waves are obtained in limiting cases. The effect of a uniform high-frequency electric field on the processes leading to the ionization of impurities by solitary waves is also investigated. Fiz. Tekh. Poluprovodn. 32, 334–337 (March 1998)     

Light absorption in aperiodic PbS/C superlattices in an electric field

Light absorption is investigated in aperiodic PbS/C Fibonacci and Thue-Morse superlattices at room temperature for two orientations of the light wave electric field. In the first case the electric field vector is directed parallel to the plane of the superlattice. In the second case there is a component perpendicular to the plane of the superlattice. Light absorption is investigated in an external electric field directed along the axis of the superlattice. Fiz. Tekh. Poluprovodn. 32, 857–859 (July 1998)