Cylindrical Semiconductor Quantum Wire Research Articles

Effect of Electron-impurity Interaction on the Optical Absorption in A Quasi-one-dimensional Electron System

In this work, we investigated the optical absorption in a quasi-one-dimensional system subjected to an external electromagnetic wave. The optical absorption coefficient was calculated by using the perturbation theory taking account of the effect of the electron - impurity interaction. The numerical result for the GaAs/AlAs cylindrical semiconductor quantum wire showed the presence of the resonant absorption peaks. The full width at half maximum (FWHM) decreased with increasing the wire radius and increases with increasing temperature. In particular, in the limit of large wire radius, the contribution of transitions between electronic subbands to the absorption spectrum becomes identical, t meaning that the system tends to behave as a bulk (there-dimensional) system when the confinement length is large. The obtained results are of significance for further studies and applications of the low dimensional systems in nano-optoelectronic devices.

Majorana zero modes in a cylindrical semiconductor quantum wire

We study Majorana zero modes properties in cylindrical cross-section semiconductor quantum wires based on the $k \cdot p$ theory and a discretized lattice model. Within this model, the influence of disorder potentials in the wire and amplitude and phase fluctuations of the superconducting order-parameter are discussed. We find that for typical wire geometries, pairing potentials, and spin-orbit coupling strengths, coupling between quasi-one-dimensional sub-bands is weak, low-energy quasiparticles near the Fermi energy are nearly completely spin-polarized, and the number of electrons in the active sub-bands of topological states is small.

Influence of Confined Optical Phonons and Laser Radiation on the Radioelectric Effect in a Cylindrical Semiconductor Quantum Wire with Parabolic Potential

Abstract. Based on the quantum kinetic equation method, the influence of confined optical phonons and laser radiation on the Radioelectric effect in a cylindrical semiconductor quantum wire with parabolic potential subjected to a dc electric field and a linearly polarized electromagnetic wave has been theoretically studied. The obtained analytical expression of the Radioelectric field (REF) depends on frequencies and amplitudes of the external electromagnetic waves, the quantum wire parameters, the temperature of the system, and especially the quantum numbers (n and m) which characterize the phonon confinement. Numerical calculations for the GaAs/GaAsAl quantum wire show the strongly impact of the confined optical phonons as well as the laser radiation on the REF magnitude and posture. The REF also has more resonance peaks in comparison with that in case of bulk phonon.

Optical Phonon Modes and Electron-optical Phonon Interaction in Core-shell Semiconductor Quantum Wires

Within the framework of the macroscopic dielectric continuum model the longitudinal optical (LO) phonon modes are derived for a cylindrical semiconductor quantum wire made of semiconductor 1 (well material) embedded in another finite semiconductor 2 (barrier material). The phonon states of modes are given by solving the generalized Born-Huang equation. It is shown that there may exist four types of longitudinal optical phonon modes according to the concrete materials forming the wire. The dispersion equations for phonon frequencies with wave-vector components parallel to the wire are obtained. After having quantized the phonon field we derive the Fröhlich Hamiltonian describing the electron--LO-phonon interaction. The influence of the thickness of the barrier layer as well as the thin metallic shell on the phonon frequencies and their interaction with electrons is studied.

Magnetic field effect on the laser-driven density of states for electrons in a cylindrical quantum wire: transition from one-dimensional to zero-dimensional behavior

The influence of a uniform magnetic field on the density of states (DoS) for carriers confined in a cylindrical semiconductor quantum wire irradiated by a monochromatic, linearly polarized, intense laser field is computed here non-perturbatively, following the Green's function scheme introduced by some of the authors in a recent work (Lima et al 2009 Solid State Commun.149 678). Besides the known changes in the DoS provoked by an intense terahertz laser field—namely, a significant reduction and the appearance of Franz–Keldysh-like oscillations—our model reveals that the inclusion of a longitudinal magnetic field induces additional blueshifts on the energy levels of the allowed states. Our results show that the increase of the blueshifts with the magnitude of the magnetic field depends only on the azimuthal quantum number m (m=0, 1, 2, …), being more pronounced for states with higher values of m, which leads to some energy crossovers. For all states, we have obtained, even in the absence of a magnetic field, a localization effect that leads to a transition in the DoS from the usual profile of quasi-1D systems to a peaked profile typical of quasi-0D systems, as e.g. those found for electrons confined in a quantum dot.

Terahertz laser-induced 1D–0D crossover in the density of states for electrons in a cylindrical semiconductor quantum wire

The effects of a linearly polarized, terahertz laser field on the density of states (DOS) for carriers confined in a cylindrical semiconductor quantum wire are investigated here within a nonperturbative scheme, based upon a Green’s function approach. In our model, the functional dependence of the DOS on energy is significantly modified in two ways: (i) an uniform blueshift with respect to the laser-free DOS; and (ii) a strong suppression, with the appearance of Franz–Keldysh-like oscillations. Interestingly, with the increase (decrease) of the laser intensity (frequency) the DOS profile evolves from the usual shape for one-dimensional (1D) systems to a discrete set of sharp peaks that resembles the DOS for quasi-zero-dimensional (quasi-0D) electrons confined in quantum dots.

Effect of a terahertz laser field on the electron-DOS in a GaAs/AlGaAs cylindrical quantum wire: finite well model

The influence of a linearly polarized terahertz laser field on the density of states (DOS) for carriers confined in a cylindrical semiconductor quantum wire is investigated here within a nonperturbative scheme, based on the Green's function approach introduced by Xu (1997 Semicond. Sci. Technol. 12 1559). In our finite potential well model, the functional dependence of the DOS on energy is significantly modified by a monochromatic, nonresonant, intense laser radiation polarized along the wire axis. Apart from a uniform blueshift with respect to the laser-free DOS, which is proportional to the laser intensity and to the inverse of the square of the frequency, a remarkable reduction of the DOS, followed by pronounced Franz–Keldysh-like oscillations above the bottom of each 1D sub-band, is obtained. The period of these oscillations is seen to depend more on the laser frequency than on the intensity. Interestingly, with an increase of the laser intensity and/or a reduction of the laser frequency, the DOS profile changes from the usual shape found in 1D electronic systems to a series of discrete peaks similar to that found in quasi-0D systems, such as quantum dots.

Electron, hole, and exciton spectra in a quantum wire crossing the quantum well

The electron, hole, and exciton energy spectra are calculated within the effective mass and rectangular potential approximations for a combined semiconductor nanoheterosystem consisting of a cylindrical semiconductor quantum wire crossing the plane quantum well. It is shown that the electron (hole) in such a system is characterized by five quantum numbers related to five degrees of freedom for a quasiparticle. The dependences of the quasiparticle energy on the quantum wire radius and the quantum well width are researched.

One phonon resonant Raman scattering in free-standing quantum wires

Abstract The scattering intensity (SI) of a free-standing cylindrical semiconductor quantum wire for an electron resonant Raman scattering (ERRS) process associated with bulk longitudinal optical (LO) phonon modes and surface optical (SO) phonon modes is calculated separately for T = 0 K . The Frohlich interaction is considered to illustrate the theory for GaAs and CdS systems. Electron states are confined within a free-standing quantum wire (FSW). Single parabolic conduction and valence bands are assumed. The selection rules are studied. Numerical results and a discussion are also presented for various radii of the cylindrical.

Franz-Keldysh effect and dynamical Franz-Keldysh effect of cylindrical quantum wires

We investigate the interband optical absorption spectra near the band edge of a cylindrical semiconductor quantum wire in the presence of a static electric field and a terahertz electric field polarized along the axis. Optical absorption spectra are nonperturbatively calculated by solving the low-density semiconductor Bloch equations in real space and real time. The influence of the Franz-Keldysh (FK) effect and dynamical FK effect on the absorption spectrum is investigated. To highlight the physics behind the FK effect and dynamical FK effect, the spatiotemporal dynamics of the polarization wave packet are also presented. Under a reasonable static electric field, substantial and tunable absorption oscillations appear above the band gap. A terahertz field, however, will cause the Autler-Townes splitting of the main exciton peak and the emergence of multiphoton replicas. The presented results suggest that semiconductor quantum wires have potential applications in electro-optical devices.

Magnetic edge states in a Kane-type semiconductor quantum wire

The energy spectra of carriers confined to a cylindrical semiconductor quantum wire in an inhomogeneous magnetic field (which is B = 0 , r < r 0 and B ≠ 0 elsewhere) are studied, by taking into account the real band structure of InSb-type semiconductors, narrow energy gap and strong spin–orbit interaction. It is found that the eigenenergy spectra for the magnetic quantum wire critically depend on the number of missing flux quantas. As the magnetic field increases it is found that the deviation of energies from the Landau levels become significant, which leads to the magnetic edge states near the boundary of the wire. The magnetic field and the radius dependence of the edge g-factor are also studied.

Energy Spectra and Lifetimes of Quasiparticles in an Open Quantum Dot Surrounded by Identical Barriers in a Cylindrical Quantum Wire

A theory of quasi-stationary states and lifetimes of electrons, holes, and excitons in an open cylindrical semiconductor quantum wire containing a quantum dot surrounded by two identical antidots (with potential barriers of finite height) is developed using the scattering matrix method. The energy spectra and lifetimes of electrons, holes, and excitons in a β-HgS/β-CdS/β-HgS/β-CdS/β-HgS nanoheterosystem are calculated and analyzed as functions of the geometric parameters of the quantum dot involved. It is demonstrated that an increase in the height of the quantum dot leads to a decrease in the energy of quasi-stationary exciton states of the Breit-Wigner type and to an increase in their lifetimes. The lifetime of exciton states is long enough for these states to be observed in the experiment.

G-Factor of carriers in Kane-type semiconductor wire

The electronic states of a Kane-type cylindrical semiconductor quantum wire with and without magnetic field are theoretically investigated and compared with those of a quantum wire of the same size. The eigenstates and eigenvalues of the Kane's Hamiltonian are obtained. Calculations are performed for a hard-wall confinement potential and electronic states are obtained as a function of the magnetic field applied along the cylinder axis. We calculated the size dependence of the effective g-values in bare GaAs, InSb and InAs nanocrystals for electrons, light holes and spin–orbital splitting holes, respectively. It has been seen that the effective g-value of the electrons and light holes are decreased while that of the spin–orbit splitting holes is increased with the increasing of quantum wires radius. It is shown that the g-value for electrons in GaAs quantum wire changes sign as a function of quantum wire radius.