A structure for enhanced terahertz emission from a photoexcited semiconductor surface

A structure that can provide enhancement of terahertz emission from a semiconductor surface excited with femtosecond laser pulses is proposed. The structure consists of a semiconductor layer on a Si substrate with metal coating on the upper surface of the layer and a Si lens attached to the bottom of the substrate. The semiconductor is excited through a hole in the coating and emits terahertz radiation through the substrate lens. We demonstrate theoretically that the proposed structure can increase the terahertz yield by orders of magnitude as compared to the previously used schemes of terahertz emission from a semiconductor surface.     

Interaction between microwave oscillation and a photoionized semiconductor plasma in a two-layer waveguide

Theoretical studies are performed on the interaction between microwave electromagnetic radiation and a photoionized semiconductor plasma in a two-layer waveguide. The interaction between the characteristic wave types of oscillation and a photoexcited semiconductor plasma is investigated. The dependences of the reflection coefficient and phase of the microwave-frequency wave on the optical radiation intensity are obtained; the effect of the surface and of the geometric dimensions of semiconductor elements on these parameters is investigated.     

Theory of the effect of a DC magnetic field on surface space-charge-wave/optical phonon instabilities in semiconductor media

A theoretical investigation has been carried out on the effect of a DC magnetic field on surface space-charge-wave instabilities caused by a drift current parallel to the surface of a doped polar semiconductor. The magnetic field is taken as perpendicular to the semiconductor surface. The dispersion relation is obtained using a generalization of the Kliewer-Fuchs specular-reflection boundary conditions. Calculated results are obtained in the non-retarded limit for two cases: (1) where a current-carrying, nonpolar semiconductor interfaces a polar insulator half-space and (2) where a current-carrying, polar semiconductor interfaces a nonpolar insulator half-space. Convective or amplifying instabilities arise because of the presence of optical phonons. Numerical results are presented for the gain as a function of frequency and magnetic field.     

Simulation of near-field images of a semiconductor surface with different carrier distributions

A method for determining the near-field image of a semiconductor surface with inhomogenous distribution of carriers has been proposed. This method is based on the linear response theory. As a result, the solution to the self-consistent Lippmann-Schwinger equation is expressed in terms of the effective susceptibility. A calculation is carried out for a semiconductor surface with inhomogenous distribution of electrons under the surface. It is shown that polarizations of both the probe field and the field at the detector in the far zone significantly affect the near-field distribution. The results obtained suggest that the orientation of aggregates (defects) under the semiconductor surface can be determined. The approach developed is universal and can be used for simulation in the scanning near-field microscopy for different types of objects under the surface.     

Time-dependent scattering of a standing surface plasmon by rapid ionization in a semiconductor

Scattering of a standing surface plasmon by rapid ionization in a semiconductor is investigated. We show that, for a standing plasmon, in contrast with a traveling plasmon, the scattering depends on the plasmon phase at the moment of ionization. By changing the moment of ionization, we can control the energy that is transferred into newly excited modes, which include a frequency-upshifted standing surface plasmon, transient outgoing radiation, and free-streaming currents with a static magnetic field in the semiconductor. The phenomena that are described open new possibilities for probing the dynamics of surface excitations in semiconductors on an ultrashort time scale.     

Temperature programmed desorption studies of CO on CdTe(110)

The thermal desorption of CO from the CdTe(110) surface was studied. The initial rate of desorption exhibits zero order kinetics with an activation energy of 2.8 kval/mol at low surface coverage rising to 4.4 kcal/mol at high surface coverage. The results may be explained in terms of the mechanism of island formation on the semiconductor surface.     

Surface electron states produced by a Rayleigh wave

The electronic properties of a semiconductor bounded by an uneven surface representing an infinitely high potential barrier are investigated. The surface irregularities are produced by a Rayleigh acoustic wave. It is shown that, on the boundary of a semiconductor, surface electron states (waves) may arise whose dispersion laws are obtained under the conditions when conduction electrons are located either in or outside the field of the acoustic wave. Existence domains of surface electron states are found that are distinguished by their physical properties. These domains are separated by a band gap whose width is determined by the height of irregularities.     

Topographical studies of semiconductor surfaces by using a combined photo-acoustoelectric method

A simple and rapid nondestructive method for a qualitative analysis of the electronic topography of semiconductor surfaces is presented, which is based on the transverse acoustoelectric effect. The method allows to follow the spatial distribution of the density and the relaxation time of energy states at the surface of the semiconductor and can be used to check its homogeneity as well as to visualize surface electronic structures.     

Spectra of magnetoplasma polaritons in a semiconductor layer on a metallic substrate

The dispersion properties of volume and surface magnetoplasma polaritons in a three-layer metal-semiconductor-insulator structure are studied. It is predicted that surface magnetoplasma polaritons propagating on the two boundaries of the semiconductor layer interact resonantly. It is shown that for a certain direction of propagation the dispersion curves of surface and volume magnetoplasma polaritons contain sections with negative dispersion. Nonreciprocal propagation of volume magnetoplasma polaritons has been observed. Losses in the semiconductor layer split the starting spectral lines into dispersion curves of two types, corresponding to forward and backward waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 38–43, January, 1988.     

Solution of the problem of surface waves in a semiconductor chip

The problem of surface waves in a semiconductor chip is solved. Under certain conditions, there are two maxima on the curve of the damping factor for an E surface wave as a function of the resistivity of the semiconductor. The first maximum corresponds to the condition that the skin depth is equal to the thickness of the chip. The second maximum corresponds to the situation in which the period of the electromagnetic field is equal to the scale time for the relaxation to the diffusion-drift equilibrium in the semiconductor. This second maximum does not occur in the case of an H wave.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 65–68, March, 1982.     

Effect of adsorption of vapours on the electrical conductivity of lycopene crystals: Evidence of a three-stage adsorption process

Upon adsorption of various vapours, the electrical conductivity of lycopene semiconductor changes appreciably This phenomenon had been used as a probe to study the adsorption and desorption processes in these polyene crystals The adsorption and desorption kinetics have been found to follow a modified Roginsky-Zeldovich relation A three-stage adsorption process has been identified The first stage gives a Lennard-Jones potential energy curve, followed by a transition over a potential barrier to the second stage of adsorption in a potential well In the third stage a deep potential energy surface is reached by activation over a second potential barrier and strongly bound complexes between the vapour molecules and the surface molecules of the crystals are finally formed.     

Interaction of guided modes and surface polaritons in a planar dielectric waveguide-semiconductor structure

In this work we have observed the interaction of waveguide modes and surface polaritons arising on the surface of a semiconductor in proximity to a dielectric wave-guide. It is shown that at frequencies for which the phase velocities of these waves coincide, there arises a resonant interaction between them, allowing the emergence of a reflected signal in the dielectric waveguide. The amplitude of this signal varies periodically with a change in the length of the semiconductor. The results that have been obtained have been able to be used as a diagnostic for semiconductor materials as well as for the excitation of surface polaritons with the aid of a dielectric waveguide.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 78–83, January, 1989.     

STM针尖和外电场在Si(111)-7×7表面单原子操纵中的作用

利用第一性原理的离散变分局域密度泛函方法,采用团簇模型（Si₃₄H₃₆-W₁₁)来模拟STM操纵Si(111)-7×7表面顶角吸附原子的过程．通过分析在进行原子操纵过程中体系的能量与电子云密度分布来研究针尖和外电场的作用．结果表明,当针尖与样品间距离较近时,利用两者间有较强的相互作用,能有效地降低脱出能的能垒高度．外电场对体系脱出能的影响与其大小及极性有关,当样品上所加正偏压增强时,脱出能曲线高度单调下降,而外电场极性为负时,反而稍有增高．仅考虑针尖和样品之间的静态电子相互作用及静电场的作用,尚不能使被操纵原子脱离样品表面．最后讨论了在Si(111)-7×7表面上进行原子操纵的其他机理.     

Electrophysical parameters of the developed surface of a nanoporous semiconductor at the equilibrium distribution of a dopant: A case of cylindrical pores

The possibility of changing surface electrophysical parameters through the directed diffusion of electroactive defects in a built-in self-consistent field near cylindrical pores in a semiconductor is discussed. The analytic expressions for the equilibrium distributions of the charged dopant, electrostatic field, and potential in the space charge region of the abovementioned structures are found in a hydrodynamic approximation. It is shown that the self-organization of mobile ions in nanoporous semiconductors in the cases under consideration leads to a considerable change in the efficiency of adsorption both of the charged particles and neutral atoms and molecules on the developed surface.     

Effect of adsorption on the surface mobility of charge carriers in a semiconductor substrate

The effect of adsorption on the carrier mobility in the near-surface region of a semiconductor substrate has been investigated within the framework of the Schrieffer model. The dependence of the carrier surface mobility on the concentration of adatoms has been determined. The systems chosen for the study are the gases adsorbed on the surface of semiconductor oxides. Empirical estimates of the surface mobility, which are based on modification of conventional volume scattering mechanisms, have been proposed.     

Ultrafast photodetectors based on the interaction of microwave radiation and a photoexcited plasma in semiconductors

The interaction of microwave radiation with the plasma in photoionized semiconductor photocells (CdS, CdSe) placed in waveguide measurement systems is investigated theoretically and experimentally. The interaction of the characteristic waveguide modes with a photoexcited semiconductor plasma is investigated. The dependence of the reflection coefficient and phase of the microwave radiation on the intensity of the optical radiation to be measured is obtained, and the influence of the surface of the semiconductor photocells on these parameters is investigated. A microwave photodetector design based on a millimeter-wave interferometer is developed. Zh. Tekh. Fiz. 68, 94–98 (November 1998)     

Negative thermal quenching of the 3.338 eV emission in ZnO nanorods

We investigate the negative thermal quenching behavior of the 3.338 eV emission in ZnO nanorods. A correlation between the 3.338 eV and the 3.368 eV (surface exciton) emissions is determined from temperature-dependent photoluminescence. The activation energies of the 3.338 eV emission, obtained using an approximated multi-level model, indicate an trap state between the two surface exciton emissions. The present study demonstrates a nondestructive and easy method to understand the surface effects on the optical properties of semiconductor nanostructures.     

Characteristic responses of a semiconductor gas sensor depending on the frequency of a periodic temperature change

A novel gas-sensing system based on a dynamic nonlinear response is reported to enhance the selectivity toward sample gases using a single detector. A periodic temperature change was applied to a semiconductor gas sensor and the resulting conductance of the sensor was evaluated by fast Fourier transformation (FFT). The dynamic nonlinear response to the sample gases was further characterized depending on the frequency of the temperature change. The characteristic sensor response under the application of a temperature change was theoretically simulated by considering the kinetics of gas molecules on the semiconductor surface.     

Surface modes of a degenerate polar pomiconductor with a surface depletion layer

Surface polariton modes of a degenerate semiconductor which has a low carrier concentration surface layer are studied in the hydrodynamic approximation. In particular, the effect of the polar phonons on the higher multipole excitats of the surface is analyzed in the long wavelength non-retarded limit.     

Transverse acoustoelectric voltage inversion and its application to semiconductor surface study: CdS

The transverse acoustoelectric voltage inversion has been observed in CdS. It is found to be due to the inversion of the semiconductor surface. The inversion layer results from a high magnitude of the dc transverse acoustoelectric voltage developed on the semiconductor surface. The acoustoelectric voltage inversion is strongly dependent on the wavelength and intensity of light illuminating the semiconductor surface, and the power input of the SAW. The sub bandgap spectral response of the transverse acoustoelectric voltage determines the positions of the surface states in the energy gap. The above bandgap spectrum determines the photon energy in which transition from bulk to surface absorption takes place and the photon energy for complete surface absorption.