Two-dimensional probe absorption spectrum in a semiconductor quantum well

We investigate the two-dimensional (2D) probe absorption spectrum in a semiconductor quantum well driven by two orthogonal standing-wave lasers. It is found that, due to the position-dependent quantum interference, the 2D spatial distribution of probe absorption spectrum can be easily controlled via adjusting the system parameters. Thus, our scheme shows the underlying probability for the applications in solid-state optic communication and transmission.     

Quantum point contact conductance in ferromagnetic semiconductor/superconductor junctions

An extended Blonder-Tinkham-Klapwijk approach is applied to study how the tunneling conductance in ferromagnetic semiconductor/s-wave superconductor (FS/SC) junction, where the FS region is a quantum wire, is manipulated by the mismatches of the effective mass between the FS and SC, spin polarization in the FS, as well as the strength of potential scattering at the interface. It is demonstrated that in the single-mode case they have different influences on the tunneling spectra.     

Tunnel barrier and noncollinear magnetization effects on shot noise in ferromagnetic/semiconductor/ferromagnetic heterojunctions

Based on the scattering approach, we investigate transport properties of electrons in a one-dimensional waveguide that contains a ferromagnetic/semiconductor/ferromagnetic heterojunction and tunnel barriers in the presence of Rashba and Dresselhaus spin-orbit interactions. We simultaneously consider significant quantum size effects, quantum coherence, Rashba and Dresselhaus spin-orbit interactions and noncollinear magnetizations. It is found that the tunnel barrier plays a decisive role in the transmission coefficient and shot noise of the ballistic spin electron transport through the heterojunction. When the small tunnel barriers are considered, the transport properties of electrons are quite different from those without tunnel barriers.     

Transport in fullerene device coupled to Cu,Ag and Au electrodes

We present an ab initio approach of the electronic transport through a single molecular junction based on C₂₀ fullerene. The electronic properties of a single molecular junction constrained within two semi-infinite metallic electrodes are largely affected by the choice of electrode material. The two-probe device formed by the mechanically control break technique has been modelled with three distinct electrode materials from group IB of the periodic table, namely copper, silver and gold. The quantum characteristics of these mechanically stable devices are obtained by utilising first-principle density functional theory together with non-equilibrium green function method. We evaluate the quantum characteristics, namely density of states, transmission spectrum, energy levels, current and conductance, which essentially determine the behaviour of a molecule linked to different electrodes. Our investigation concludes that copper, silver and gold electrode configuration in conjunction with C₂₀ fullerene behaves as metallic, non-metallic and semi-metallic in nature, respectively.     

Josephson current through a ferromagnetic semiconductor/semiconductor/ferromagnetic semiconductor structure

We theoretically calculate the Josephson current for two superconductor/ferromagnetic semiconductor (SC/FS) bilayers separated by a semiconductor (SM) layer. It is found that the critical Josephson current I_C in the junction is strongly determined by not only the relative orientations of the effective exchange field of the two bilayers and scattering potential strengths at the interfaces but also the kinds of holes (the heavy or light) in the two FS layers. Furthermore, a robust approach to measuring the spin polarization P for the heavy and light holes is presented.     

Magnetoconductance oscillations in semiconductor-superconductor junctions with a laterally isolating barrier layer inside semiconductor region

The oscillatory characteristics of magnetoconductance for a junction composed of a superconductor and a semiconductor, in which two parallel quantum wave guides are coupled with each other through a potential barrier layer, are studied systematically. To model the imperfectness of the interface, we introduce a function scattering potential barrier lying close to the interface of the junction. The magnetoconductance oscillations (MCO) in this system stem from two sources: one is the interference of wave functions of quasi-particles due to multiple Andreev reflections at the interface; the other is attributed to the variation of the number of the propagation modes when introducing the isolating barrier layer. The introduction of the isolating layer in the quantum wave-guides strongly modifies MCO. We also present a physical picture for the MCO based on a phenomenological argument. The theoretically fitted results are in good agreement with numerical ones.Received: 21 March 2003, Published online: 4 August 2003PACS: 73.40.-c Electronic transport in interface structures - 74.80.Fp Point contact; SN and SNS junctions - 73.21.Hb Quantum wires - 85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)     

Interplay of Rabi oscillations and quantum interference in semiconductor quantum dots

We investigated the manifestation of Rabi oscillation in the coherent dynamics of excitons in self-assembled semiconductor quantum dots. The Rabi oscillation phenomenon was directly observed as a function of the input pulse area. Furthermore, by performing wave packet interferometry in the nonlinear excitation regime, we discover a new type of quantum interference phenomenon, resulting from the interplay between Rabi oscillation and quantum interference.     

Observation of the intraexciton Autler-Townes effect in GaAs/AlGaAs semiconductor quantum wells

The near-infrared transmission of a semiconductor multiple quantum well is probed under intense terahertz illumination. We observe clear evidence of the intraexcitonic Autler-Townes effect when the terahertz beam is tuned near the 1s-2p transition of the heavy-hole exciton. The strongly coupled effective two-level system has been driven with terahertz field strengths of up to 10 kV/cm resulting in a Rabi energy of ≈0.6 times the transition energy. The induced near-infrared spectral changes at low intensities are qualitatively explained using a basic two-level model.     

Transient electron population and optical properties in a semiconductor quantum well

We investigate the transient behaviors of the dispersion and the absorption in a three-level GaAs/AlGaAs semiconductor quantum well system. It is found that the Fano interference and the energy splitting affect the transient behaviors dramatically, which can be used to manipulate efficiently the gain-absorption coefficient and group velocity of the probe field. The dependence of transient electron population on the Fano interference and the energy splitting is also discussed.     

Spin dependent Andreev reflection in ferromagnetic semiconductor/d-wave superconductor ballistic junction

The Andreev reflection (AR) probability and transmission of quasiparticles in ferromagnetic semiconductor/d-wave superconductor (FS/DS) ballistic junctions are studied based on an extended Blonder–Tinkham–Klapwijk (BTK) theory. It is shown that the dependence of AR probability and pair potential on the spin orientation of incident quasiparticles for the heavy holes is much different from that for light holes due to the different mismatches in the effective mass and Fermi velocity between FS and DS. The junction conductance is dominated by the quasiparticles which undergo AR processes with the largest probability, and this provides a method for measuring the spin polarization in FS.     

Control of two-dimensional electron population in a semiconductor quantum well

We investigate the two-dimensional (2D) electron population in a semiconductor quantum well. It is found that, due to the position-dependent quantum interference, the 2D spatial distribution of electron population can be easily controlled via adjusting the system parameters. Thus, our scheme shows the underlying probability for the applications in solid-state optoelectronics.     

Investigation of electronic coupling in semiconductor double quantum wells using coherent optical two-dimensional Fourier transform spectroscopy

We investigate electronic coupling in asymmetric semiconductor double quantum wells using a new spectroscopy method, optical two-dimensional Fourier transform (2D-FT) spectroscopy. Measurements on two samples with different barrier thicknesses show drastically different 2D-FT spectra. We compare these measurements to conventional one-dimensional four-wave-mixing measurements, highlighting the unique advantages of the 2D-FT spectroscopy. An oscillatory behavior in the intensity of the cross peaks as a function of the mixing time is observed. This oscillation is attributed to interference between different quantum mechanical pathways, and its features are determined by the non-radiative Raman coherence between dipole-forbidden states.     

Spin-dependent transmission of holes through a semiconductor quantum wire with multiple stub

The spin transport of holes through a quantum wire made of many identical T-shaped diluted magnetic semiconductor/semiconductor units is investigated theoretically. The spin-down and spin-up transmission coefficients have been studied as a function of stub parameters. The spin-up transmission coefficient as a function of the stub length is extremely negligible, in the case of multiple-stub quantum wire, while the spin-down transmission coefficient shows a nearly periodic behaviour with regions of large transmission separated by forbidden bands. The spin polarization switches periodically between one and zero as the stub length is changed and shows a square-wave pattern.     

Spin-dependent shot noise in diluted magnetic semiconductor/semiconductor heterostructures with a nonmagnetic barrier

We investigate quantum size effect on the spin-dependent shot noise in the diluted magnetic semiconductor (DMS)/semiconductor heterostructure with a nonmagnetic semiconductor (NMS) barrier in the presence of external magnetic and electric fields. The results demonstrate that the NMS barrier plays a quite different role from the DMS layer in the electron transport process. It is found that spin-down shot noise shows relatively regular oscillations as the width of DMS layer increases, while the spin-up shot noise deceases monotonically. However, as the width of NMS layer increases, the spin-down shot noise displays irregular oscillations at first and then decreases while the spin-up shot noise decreases at a quite different rate. The results indicate that the shot noise can be used as a sensitive probe in detecting material type and its size.     

场助InGaAsP/InP异质结半导体光电阴极的研究

本文通过对InGaAsP/InP场助异质结半导体光电阴极的材料生长、场助肖特基结的制备及阴极激活等工艺的系统研究,研制出具有较高光谱响应的半导体光电阴极,生长出优于文献报道的晶格失配率标准的材料,得到相当80年代国际水平理想因子值的场助肖特基结,用实验数据介绍提高量子效率数量级的方法和条件.研究结果表明场助异质半导体光电阴极是在红外波段很有潜力的光电发射体.     

Intrinsic Hall effect and separation of Rashba and Dresselhaus spin splittings in semiconductor quantum wells

We have proposed a method to separate Rashba and Dresselhaus spin splittings in semiconductor quantum wells by using the intrinsic Hall effect. It is shown that the interference between Rashba and Dresselhaus terms can deflect the electrons in opposite transverse directions with a change of sign in the macroscopic Hall current, thus providing an alternative way to determine the different contributions to the spin--orbit coupling.     

Circular-to-linear and linear-to-circular conversion of optical polarization by semiconductor quantum dots

We report circular-to-linear and linear-to-circular conversion of optical polarization by semiconductor quantum dots. The polarization conversion occurs under continuous wave excitation in the absence of any magnetic field. The effect originates from quantum interference of linearly and circularly polarized photon states, induced by the natural anisotropic shape of the self-assembled dots. The behavior can be qualitatively explained in terms of a pseudospin formalism.     

Opto-thermionic refrigeration in semiconductor heterostructures.

Combining the ideas of laser cooling and thermionic cooling, we have proposed an opto-thermionic cooling process, and investigated its cooling effect caused by the light emission from a quantum well embedded into a semiconductor pn junction. For a GaAs/AlGaAs opto-thermionic refrigerator in which the Auger recombination is the major nonradiative process, cooling can be achieved in a finite range of bias voltage. Using the measured values of the Auger coefficient, our calculated cooling rate is at least several watts/cm(2).     

A comparative study of electron transport in benzene molecule covalently bonded to gold and silicon electrodes for pioneering the electron transport properties of silicon quantum dot-molecule hybrid polymers

In order to pioneer the electron transport properties of silicon (Si) quantum dot-molecule hybrid polymers, we investigate the electron transport properties of the benzene molecule in silicon (Si) semiconductor electrodes, based on nonequilibrium Green's function (NEGF) method coupled with density functional theory (DFT), in comparison with conventional gold (Au) metal electrodes, with three different anchoring linker groups: thiol for dithiol-benzene (DTB), methylene for dimethyl-benzene (DMB), and direct bonding for benzene (Ph). It is interestingly found that, due to band gap nature of the Si semiconductor electrodes, the molecular junctions with the Si electrodes show no current up to the bias voltage of around 0.8 V. In addition, the DTB molecular junctions in the Si semiconductor electrodes connected with Si–S bond show higher conducting properties than other DMB and Ph molecular junctions directly coupled to the electrodes with the Si–C bonds (DMB < Ph < DTB). The electron transport properties of the molecules in the two different electrodes are analyzed on the basis of the understanding transmission spectra, projected density of states (PDOS), and molecular orbitals. We believe that the use of thiol linker may open new possibility in the molecular electronics with the Si semiconductor electrodes and the Si QD-molecule hybrid polymers concept.     

Solid ionic conductor/semiconductor junctions for chemical sensors

The potential drop at solid ionic conductor/semiconductor contacts responds to partial pressure changes of gases since the Fermi level of the semiconductor depends on the adsorbed species and equilibrates with that of the ionic conductor. In an alternative consideration, the semiconductor acts as a catalyst for the reaction of the mobile ions of the solid ionic conductor with the adsorbed species. The junction is employed as a chemical sensor for the detection of CO₂ by using NASICON as solid electrolyte and doped SnO₂ as semiconductor. The device is applicable even at room temperature with fast response time. Mechanisms of the response of the junction to gases are discussed in detail. The principle of employing solid ionic conductor/semiconductor junctions for sensors is in general applicable for many gases.On leave from the Institute of Physics, Academy of Sciences, Chernogolovka, Russia