Interband light absorption in size-confined systems in uniform electric fields

A simple approach to calculation of the interband absorption coefficient in a uniform electric field is developed. This approach provides a means for studying the special features of electroabsorption in a wide class of semiconductor systems on the basis of the most general relationships. The approach is used to study the electroabsorption in two-dimensional systems with different profiles of their one-dimensional potential, quantum wells, and superlattices in magnetic fields.     

Variable optical buffer using slow light in semiconductor nanostructures

A compact variable all-optical buffer using semiconductor quantum dot (QD) structures is proposed and analyzed. The buffering effect is achieved by slowing down the optical signal using an external control light source to vary the dispersion characteristic of the medium via an electromagnetically induced transparency effect. We present a theoretical investigation of the criteria for achieving slow light in semiconductor QDs. A QD structure in the presence of strain is analyzed with the inclusion of polarization-dependent intersubband dipole selection rules. Experimental methods to synthesize and the measurements of coherent properties in state-of-the-art QDs are surveyed. Slow-light effects in uniform and nonuniform QDs are compared. Finally, optical signal propagation through the semiconductor optical buffer is presented to demonstrate the feasibility for practical applications.     

Interband magnetooptic absorption line shape in bismuth

The results of an investigation of the transmission of a symmetric bismuth stripline at T=80 K at the laser wavelength λ=10.6 μm in magnetic fields up to B=8 T are reported. A set of parameters is obtained for the energy spectrum of the L electrons of bismuth by modeling the shape of the experimental curve on the basis of a modified Baraff model. The values of the parameters in the McClure-Choi model are found from an analysis of the field positions of the maxima of the mageto-optic oscillations. Fiz. Tekh. Poluprovodn. 31, 416–419 (April 1997)     

Spectral interferometry of semiconductor nanostructures

Fourier transform spectral interferometry is applied to measure both amplitude and phase of the electric field in different types of semiconductor nanostructures, thus determining the real and imaginary parts of the dielectric function. The importance of measuring the phase is shown and discussed in three studies. First, the phase measurement is used to access directly the refractive index across excitonic resonances in bulk GaAs and AlGaAs-GaAs quantum wells, with unprecedented resolution. Second, we measure the density dependence of the full dielectric function across a Fano resonance in bulk GaAs and show that this allows us to obtain some information on the collisional broadening of the usually hidden linewidth of the coupled exciton/continuum. Third, the phase is studied in a complex heterostructure, a semiconductor microcavity. We investigate and discuss the effect of the cavity detuning and of the excitation density     

Exciton states in semiconductor spherical nanostructures

The results of theoretical studies of the energy spectra of excitons moving in semiconductor spherical quantum dots are described. The contributions of the kinetic electron and hole energies, the energy of the Coulomb interaction between an electron and hole, and the energy of the polarization interaction between them to the energy spectrum of an exciton in a quantum dot with a spherical (quantum dot)-(insulator medium) interface is analyzed.     

Formation of three-dimensional ZnSe-based semiconductor nanostructures

Nanostructures consisting of a 10-nm-thick sacrificial layer of ZnMgSSe and a 20-nm-thick stressed bilayer of ZnSSe/ZnSe were grown by molecular-beam epitaxy on GaAs substrates. Upon removal of the sacrificial layer by selective etching, multiwall ZnSSe/ZnSe microtubes were formed.     

Recombination statistics and kinetics in semiconductor nanostructures

A new approach to describing the observed features of recombination in semiconductor nanostructures is suggested. In addition to radiative exciton recombination, a nonradiative channel of exciton Auger recombination involving local interface states is taken into account. Recombination statistics and kinetics in semiconductor nanocrystals are considered both for low and high densities of local interface states. The case of a low excitation level, where a statistical approach to recombination in isolated nanocrystals is no longer valid, is analyzed. It is shown that the presence of nonradiative exciton Auger recombination accounts both for the linear dependence of photoluminescence intensity on the excitation level and for the low photoluminescence quantum efficiency.     

Surface-enhanced Raman scattering from semiconductor nanostructures

正Developing the surface-enhanced Raman scattering(SERS)substrate from noble metals to semiconductors would bring the SERS more promising applications in biomedicine detection.Based on the photo-induced charge transfer(PICT)mechanism the SERS model in the semiconductor-molecule system was built up.The analytical solution of the contribution from PICT to the molecular polarizability tensor was presented according to calculation of quantum mechanics,and the results suggested that arising SERS from the nanostructured Si substrate is possible.Experimental observation revealed that the numerous hydrogen atoms on the surface of the Hterminated Si nanowire(H-SiNW)arrays may serve as electron sink,and play a critical role in promoting efficient PICT and enable the SERS effect.The evident Raman enhancement of the standard probe Rodamine 6G(R6G),dye(Bu4N)2[Ru(dcbpyH)2-(NCS)2](N719),and the 4-aminothiophenol(PATP)from such substrates were detected.1 A significant enhancement of b2 modes could be observed from PATP chemisorbed on the H-SiNWs substrate,which indicated that a strong PICT process had taken place in the system.     

Carrier transport mechanisms in semiconductor nanostructures and devices

Semiconductor nanostructures have gained importance due to their potential application in future nanoelectronic devices. For such applications, it is extremely important to understand the electrical properties of semiconductor nanostructures. This review presents an overview of techniques to measure the electrical properties of individual and clusters of semiconductor nanostructures using microcopy based techniques or by fabricating metallic electrical contacts using lithography. Then it is shown that current–voltage (I–V) characteristics can be used to determine the conduction mechanism in these nanostructures. It has been explained that various material parameters can be extracted from I–V characteristics. The frequently observed conduction mechanism in these nanostructures such as thermally activated conduction, space charge limited current (SCLC), hopping conduction, Poole Frenkel conduction, Schottky emission and Fowler Nordheim (FN) tunneling are explained in detail.     

Slow light propagation without absorption based on intersubband transitions in a semiconductor quantum well

When semiconductor quantum wells(SQWs) interact with lasers,the group velocity of the low-intensity light pulse is studied theoretically.It is shown that by adjusting the parameters,slow light propagation of the probe field can be exhibited in such a system.Meanwhile,the probe absorption-gain spectra can be changed from absorption to zero,i.e.,electromagnetically induced transparency(EIT).It is easy to observe the light propagation experimentally,and it leads to potential applications in many fields of solid-state quantum information,for example,optical switching,detection and quantum computing.     

Dielectric function of quasi-2D semiconductor nanostructures

The spatial and temporal dispersion of the dielectric function of the electron gas in quasi-2D quantum nanostructures has been studied. Analytical expressions for the dielectric function for a quantum well in the form of a δ function and a rectangular well of finite depth are derived for the first time. A criterion for transition to strictly 2D and strictly 3D cases was obtained.     

准一维半导体纳米结构的电子显微学研究

本文总结了近年来我们在功能准一维纳米结构材料研究方面所获得的一些有意义的结果。借助于现代电子显微镜技术，不仅研究了硅、氮化稼、氧化锌等一维纳米材料的形貌和显微结构，还研究了其一维择优生长机理及小尺度效应。尤其是利用高能量分辨电子能量损失谱、高角环形暗场探头等先进技术，解决了一个传统X－光等结构分析手段所不能解决的难题，分析了一种SiOx/SiC复合纳米电缆的成份与结构。     

Interband absorption of long-wavelength radiation in δ-doped superlattices based on single-crystal wide-gap semiconductors

A new type of superlattice formed in a single-crystal nondegenerate, wide-gap semiconductor by a sequence of pairs of closely spaced, δ-doped donor and acceptor layers is proposed. It is shown that because of the superstrong electric fields generated between these δ-doped layers, the electroabsorption of long-wavelength radiation is determined by tunneling optical transitions of electrons from the heavy-hole band (in contrast to the case of moderately strong fields when the electroabsorption is determined by light holes). The magnitude of the electroabsorption is close to the interband absorption for light and is virtually independent of the photon energy up to the far-infrared region. It was found that in the proposed InSb-based superlattice the absorption in superstrong fields can exceed 10³ cm⁻¹ up to radiation wavelengths approximately equal to 50–100 μm. It is noted that because of the spatial separation of the photogenerated electrons and holes, their lifetime and the long-wavelength sensitivity of such a superlattice have giant values. Fiz. Tekh. Poluprovodn. 32, 221–226 (February 1998)     

Photon properties of light in semiconductor microcavities

Properties of atom-like emitters in cavities are successfully described by cavity quantum electrodynamics(cavity-QED).In this work,we focus on the issue of the steady-state and spectral properties of the light emitted by a driven microcavity containing a quantum well (QW) with the excitonic interactions using simulation of fully quantum-mechanical treatment.The system is coherently pumped with laser,and it is found that depending on the relative values of pumping rate of stimulated emission,either one or two peaks close to the excitation energy of the QW or to the natural frequency of the cavity are shown in the emission spectrum.Furthermore,the nonclassical proprieties of the emitted photon have been investigated.This excitonic system presents several dynamical and statistical similarities to the atomic system,in particular for the bad-cavity and good-cavity limits.The results show that the photon emission can be significantly amplified due to the coupling strength between a single emitter and radiation field in the microcavity,and it is concluded that the present semiconductor microcavity system may serve as a QW laser with low threshold.     

Quantum light sources from semiconductor

Semiconductor provides a physics-rich environment to host various quantum light sources applicable for quantum information processing. These light sources are capable of deterministic generation of non-classical photon streams that demonstrate antibunching photon statistics, strong indistinguishability, and high-fidelity entanglement. Some of them have even successfully transitioned from proof-ofconcept to engineering efforts with steadily improving performance[ 1]. Here, we briefly summarize recent efforts and progress in the race towards ideal quantum light sources based on semiconductor materials. The focus of this report will be on group III–V semiconductor quantum dots, defects in wide band-gap materials, emitters in two-dimensional van der Waals layered hosts, and carbon nanotubes, as these systems are well-positioned to benefit from recent breakthroughs in nanofabrication and materials growth techniques.     

Self-organization of nanostructures on planar and patterned high-index semiconductor surfaces

In order to directly control the size and in particular the position of nanostructures naturally formed on high-index semiconductor surfaces during molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE), the growth on patterned high-index GaAs substrates is investigated. During MBE of (AlGa)As on patterned GaAs (311)A substrates, a new phenomenon in the selectivity of growth has been found to form a fast growing sidewall on one side of mesa stripes oriented along the [01-1] direction. Preferential migration of Ga adatoms from the mesa top as well as the mesa bottom toward the sidewall develops a smooth convex curved surface profile without facets. This unique growth mode that does not occur for the perpendicular stripe orientation nor on other patterned GaAs (n11)A and B substrates is stable for step heights down to the quantum size regime to produce lateral quantum wires on patterned GaAs (311)A substrates. Quantum confinement of excitons in the wires has been demonstrated by the transition from two-dimensional to magnetic confinement with increasing magnetic field. For device applications it is important that the wires can be stacked in the growth direction without any increase in interface roughness or wire size fluctuations, indicating a self-limiting lateral growth mechanism. Finally, in strained layer epitaxy, (InGa)As islands can be selectively placed on the mesa top and bottom leaving entirely free the curved part along the fast growing side-wall.     

All-optical sampling utilising two-photon absorption in semiconductor microcavity

A highly-efficient optical sampling system based on two-photon absorption in a semiconductor microcavity is presented. The sensitivity of the sampling system is calculated to be 0.1 mW/sup 2/ with a temporal resolution of 2 ps.     

Magnetic nanostructures and nanodevices with a semiconductor or dielectric spacer

Magnetic properties of nanoscale magnetic-layer systems using FeNi, Co, FeMn, Al₂O₃, and SiC layers are studied experimentally. The dependence of magnetic behavior on the system geometry and parameters is addressed. Ferromagnet-semiconductor exchange coupling subject to the amplitude of an applied magnetic field is revealed. It is found that the magnetic behavior of the nanostructures varies in a nonlinear manner with applied magnetic field. Spin-tunneling magnetoresistance is observed in magnetic-layer junctions containing an Al₂O₃ spacer. In-plane-conduction magnetic-field sensors using an Al₂O₃ or a SiC spacer are fabricated and tested.Translated from Mikroelektronika, Vol. 34, No. 1, 2005, pp. 56–64.Original Russian Text Copyright © 2005 by Kasatkin, Muravjev, Plotnikova, Pudonin, Azhaeva, Sergeeva, Khodzhaev.