Amplification of magnetoelastic Love waves by interaction with carrier waves in a layered composite

Magnetoelastic Love waves (m.e.l.w.s), propagating in a piezoelectric-layered metal-coated magnetic substrate, may be amplified by interaction with carrier waves in an adjacent semiconductor. The amplification characteristics of m.e.l.w.s. in the magnetoelastic coupling region between magnetostatic surface waves and piezoelectric Love waves, are presented here using numerical calculations.     

Signal processing in acoustic surface-wave devices

The Rayleigh surface-wave mode propagates on the surface of suitable elastic solids with velocity independent of frequency at about 10-5 times the speed of light and an attenuation of about 1.5 dB for 104 wavelengths. Thus as a delay line it is far more compact, has much less attenuation, and can be much cheaper than electromagnetic delay lines. Piezoelectric elastic solids permit the launching and detection of the waves by electrodes on the surface. Fabrication technology is similar to that used for monolithic semiconductors and amplification is possible by interaction with carriers in a semiconductor surface layer. Parametric interactions can be used to perform convolution of two signals. The feasibility of deflecting and modulating light beams also has been demonstrated. This rapidly developing art can today produce delay lines, filters, pulse compressors and expanders, and pulse-sequence generators and decoders, and in the future may perform convolution, correlation, and light-beam manipulation in small, economical, low-power structures.     

The theory of the interaction of drifting carriers in a semiconductor with external traveling-wave circuits

The interaction between slow electromagnetic waves and drifting carriers in a semiconductor is analyzed including mechanisms important and peculiar to the semiconductor device. The growth rate coefficients, excitation amplitudes, and phase are found using a modification of Pierce's one-dimensional model of the traveling-wave tube. A technique for calculating a growing mode criterion is presented.     

Role of sulfide ion solvation in the modification of GaAs surface electronic structure

A model is proposed wherein the interaction of the adsorbate (sulfide ion) with the GaAs surface is considered with allowance made for the influence of the solvation shell. It is shown by quantum-chemical calculations that the solvation of the adsorbate by different solvent molecules results in the variation of the relationship between the adsorbate ability to accept and donate electrons in chemical reactions, which has a determining effect on the adsorbate interaction with the semiconductor surface states and, thus, on the modification of the electronic structure of the semiconductor surface.     

Electromagnetic waves and oscillations in the layered semiconductor-dielectric-semiconductor structure

Theoretical and numerical studies of the electromagnetic properties of the layered semiconductor — dielectric — semiconductor (SDS) structure was carried out. It was shown that the weak damping guide and surface waves may exist in this structure and retardation of surface waves may be several times more than for the semiconductor — dielectric (SD) interface. If this structure contains reflections it leads to the formation of high Q-factor resonance oscillations. It was found that at the beginning of intermode coupling of two surface oscillations in the studied resonance structure, hybrid surface oscillations with near resonance frequencies are formed. Their electromagnetic field components along the wave propagation direction are orthogonal to each other and modulated along the SD interface by orthogonal envelopes.     

基于半导体等离子体频率光学调控的太赫兹波调制系统

介绍了一种太赫兹波光学调制系统,该系统首先通过刀片与半导体之间的狭缝实现太赫兹波和太赫兹表面等离子体波之间的耦合,然后通过改变照射到本征半导体表面的光强用以调控半导体表面的等离子体频率,使得半导体表面的等离子体频率在有光照和无光照条件下分别大于和小于其上传输的太赫兹表面等离子体波的频率,从而实现对在半导体表面传输的太赫兹表面等离子体波以及由其耦合出的太赫兹波的强度调控。该调制方法与传统方法相比具有调控频带宽、速度快、成本低、常温工作等优点,可用于太赫兹波通讯。仿真和实验结果进一步验证了该调制系统应用的可行性。     

Carrier waves in semiconductors I: Zero temperature theory

A detailed treatment of the space-charge waves or carrier waves which are associated with drifting carriers in a semiconductor is given. These waves have a phase velocity comparable to that of the drifting carriers, but normally have very high loss. This dielectric relaxation loss may be radically decreased by utilizing the interaction between two sets of carriers, working with semiconductors of small cross section, or semiconductors placed against high permittivity materials. Gain may be obtained by using special materials such as GaAs, or by the use of interactions between two sets of carriers in the presence of a magnetic field. The treatment given neglects the effect of diffusion so as to keep the mathematics simple and emphasize the physics of the problem. In a later paper, methods of taking diffusion into account will be given.     

表面波飞机结冰传感器的研究

首先分析了覆盖冰层的各向同性半无限大弹性体中的声表面波(SAW),求得了声表面波波速与冰层厚度间的关系.结果表明,当冰层厚度为0时,求得的波速与没有冰层覆盖相对应的半无限大弹性体的声表面波波速相同;当冰层厚度不断增加时,求得的声表面波波速趋向于冰层中的波速.随后分析了基体是各向同性无限大弹性板的情况.计算结果表明,由于弹性板与冰层的相互作用,实际振动会出现多个声表面波模态和相应的波速.     

Nonlinear interaction of acoustic surface waves with carriers

We calculate the 2nd-order signal generation due to the space-charge nonlinearity induced by two interacting surface waves in a piezosemiconducting material. Using the Bleustein?Gulyaev mode as a typical example, it is shown that this 2nd-order term is not zero for two oppositely travelling surface waves of the same frequency ? in the absence of electron drift. This calculation clearly shows that this nonzero signal arises from the decrease in the ultrasonic electric field toward the interior of the sample. The general result can be extended easily to other types of elastic surface waves. Complementary experiments are also reported on the interaction of surface waves propagating in the same direction, and it is shown that there is a satisfactory agreement between the experimental data and the results of the analysis.     

Phase conjugation on the surface of optically excited ZnO

The feasibility of phase conjugation in excited semiconductor media is shown both theoretically and experimentally. For the first time, phase conjugation of a light wave (nitrogen laser) with a photon energy equal to half the exciton radiative recombination energy in the medium (ZnO epitaxial films) at room temperature is revealed. The spectral dependences of the phase conjugation signal are studied. The quadratic interaction between the electromagnetic and exciton waves in a semiconductor is suggested as a possible mechanism of this effect.     

Signal Processing by Parametric Interactions in Delay-Line Devices

A new type of signal-processing device which employs the parametric interaction between surface or volume acoustic waves passing in opposite directions through an acoustic delay line is described. These devices are capable of giving the real-time convolution of two modulated signals, and the time inversion of an arbitrary signal. As one signal acts as the reference for the other, a virtually infinite range of electronically variable signal-processing functions, such as recognition of digital codes, pulse compression of an FM chirp, and the realization of a fast Fourier transform, is possible. Early devices which employed the nonlinearity of the acoustic medium tended to give outputs of the order of 60 dB less than the input signal. Recent developments, in which a semiconductor placed near the piezoelectric medium interacts with the acoustic wave, have yielded results where the loss from input to output is of the order of 30 dB.     

On the Theory of Shielded Surface Waves

An analysis is given for the modes which will be excited between two parallel impedance boundaries. It is shown that, for inductive-type surfaces, two of these modes have a surface wave character even though the structure is bounded in the transverse dimension. The interaction between these surface waves and the accompanying waveguide modes is discussed for this model which is admittedly highly idealized.     

Ultrasonic effects in piezoelectric semiconductors

Several interesting phenomena involving the interaction of ultrasonic waves and electrons have been observed in piezo-electric semiconductors. These include the processes of ultrasonic amplification and nonlinear harmonic generation, which are manifestations of the action of electrons on ultrasonic waves. The reaction upon the electrons as a result of their strong coupling to ultrasonic waves is manifested by the phenomena of current saturation and current oscillations in amplifying semiconductor crystals. We discuss the principle of acoustoelectric amplification and the role it plays in these effects. The difference between the amplification process and the Cerenkov emission of sound waves is emphasized. The generation of harmonics of the sound wave due to the nonlinear transport properties of the electrons is reviewed. Various models of current saturation are considered, including an elementary treatment of the role of acoustoelectric fields. A discussion is given of the possibility of propagating collective sound waves under amplifying conditions and the role that this may play in the current oscillations in cadmium sulphide.     

Theory of space-harmonic traveling-wave interactions in semiconductors

Strong coupling can be obtained between slow space-charge waves in thin biased semiconductors and long-wavelength microwave fields, if the semiconductor is overlaid with an insulated periodic mosaic of tiny metal stripes. Microscopic field perturbations are represented by a set of slow space-harmonic waves traveling in opposite directions, with a standing-wave interference pattern which matches the periodicity of the mosaic. When the carrier drift velocity is approximately synchronized with one of the space-harmonic waves, interaction is enhanced, space-charge waves may be induced, negative-resistance effects may appear, and power may be coupled from the semiconductor into external microwave networks. Theory indicates that the principle can be used to obtain microwave amplification or oscillation in thin biased layers of normal semiconductors such as silicon or germanium. It may also be possible to couple efficiently in this way to traveling Gunn-effect domains in extensive thin layers of gallium arsenide.     

Generation of surface electromagnetic waves in semiconductors under the action of femtosecond laser pulses

It is demonstrated that intense photoexcitation of the surface of a semiconductor with femtosecond laser pulses can induce fundamental changes in its optical response and ensure conditions for the generation of surface electromagnetic waves of various types. The connection between electronic processes initiated in the surface layer by photoexcitation and the formation of periodic surface microstructures observed in experiments on irradiation of Si targets is considered. The importance of photoemission in the processes taking place under ultrashort excitation is confirmed.     

半导体激光并超短波治疗慢性前列腺炎的临床观察

目的：观察半导体激光治慢性前列腺炎的临床疗效。方法：将患者140例随机分为2组．治疗组76例,采用半导体激光并体外短波对会阴部治疗;对照组64例,单纯采用体外短波治疗。结果：治疗组有效率为89．2％;对照组有效率为76．5％。两组比较差异显著（P＜0．05）。结论：半导体激光照射治疗慢性前列腺炎可明豆糖高疗效。     

Application of the transverse acoustoelectric effect to studying silicon surface charging upon water adsorption

Water adsorption on a silicon surface in a layered Si-LiNbO₃ structure with an air gap is studied using the transverse acoustoelectric effect on surface acoustic waves. A generalized analysis of measurements of the transverse acoustoelectric effect makes it possible to determine the initial band bending of the Si surface, its changes during gas cycles, hence, the sign and charging kinetics of Si upon H₂O adsorption. Depending on the properties of the semiconductor surface defects, both the donor and acceptor nature of the interaction of H₂O with Si are observed. For samples with a thermal oxide, the donor-type interaction occurs; for samples with a natural oxide, both interaction types take place. Based on the used physical model of oxide charging upon exposure to an adsorbate, a comprehensive methodical approach is proposed, which allows the targeted development of acoustoelectronic structures for sensor applications.     

A simulation model for cathodoluminescence in the scanning electronmicroscope

An improved three-dimensional model for simulating cathodoluminescence (CL) in a semiconductor under electron-beam irradiation is described. The Monte Carlo method is used to simulate electron-beam-semiconductor interaction while F. Berz and H.K. Kuiken's (1976) formulation is used to obtain the excess carrier distribution. Optical losses of photons both within the semiconductor and at the semiconductor-air interface are also accounted for in this model. This model has been used to simulate the CL intensity as a function of electron-beam voltage, beam incidence angle, surface recombination velocity, diffusion length, absorption coefficient, and surface dead-layer thickness. The radiation patterns over the top face of a specimen with flat geometry are also simulated     

Propagation of surface polaritons and total electromagnetic wave transmission through layered structures

Dispersion relations of coupled magnon-plasmon surface electromagnetic waves propagating along the interface between antiferrodielectric and uniaxial semiconductor are considered. Total transmission of infrared wave trough such layered structure induced by resonant excitation of the surface wave is investigated.     

Semiconductor surface study by transverse acoustoelectric voltage using surface acoustic waves

Electrical properties of semiconductor surfaces can be determined by measuring the transverse acoustoelectric voltage. This voltage is produced by the interaction of the surface acoustic wave propagating on a piezoelectric substrate and the carriers on semiconductor surface placed in proximity. Using 110 MHz LiNbO₃ delay lines, the transverse acoustoelectric voltage has been measured across CdS and Si, the surface properties of which are varied by different light illumination. Detailed study of the voltage waveform reveals the type of traps and the amount of charge in the traps. The method is simple, needs no contacts to the sample, and is sensitive.