InAs Quantum Wires Research Articles

A theoretical evaluation of optical properties of InAs/InP quantum wire with a dome cross-section

In the present work, we have theoretically studied the optical properties of a InAs quantum wire with dome cross section. We have used a numerical method which is based on a combination of coordinate transformation and the finite difference method. For this purpose, we have used analytical expressions for optical properties obtained by the compact-density matrix formalism. We have evaluated the linear, non-linear and the total absorption coefficients between the ground state for electron and heavy hole as a function of photon energy. The linear, non-linear and total refractive index changes are also investigated. These optical properties are determined with varying the incident optical intensity and the height of the wire.

Magnetic field inducing Zeeman splitting and anomalous conductance reduction of half-integer quantized plateaus in InAs quantum wires

We report on magnetic field dependence of half-integer quantized conductance plateaus (HQPs) in InAs quantum wires. We observed HQPs at zero applied magnetic field in InAs quantum wires fabricated from a high-quality InAs quantum well. The application of in-plane magnetic field causes Zeeman splitting of the HQP features, indicating that the origin of the observed HQP is not spontaneous spin polarization. Additionally we observe that conductance of the split HQPs decreases gradually as the in-plane magnetic field increases. We finally assume electron-electron interaction as a possible mechanism to account for the zero-field HQPs and the anomalous field dependence.

Arbitrary qubit transformations on tuneable Rashba rings

An exact solution is presented for the time-dependent wavefunction of a Kramers doublet which propagates around a quantum ring with tuneable Rashba spin-orbit interaction. By propagating in segments it is shown that Kramers-doublet qubits may be defined for which transformations on the Bloch sphere may be performed for an integral number of revolutions around the ring. The conditions for full coverage of the Bloch sphere are determined and explained in terms of sequential qubit rotations due to electron motion along the segments, with change of rotation axes between segments due to adiabatic changes in the Rashba spin-orbit interaction. Prospects and challenges for possible realizations are discussed for which rings based on InAs quantum wires are promising candidates.

Suppression of Coulomb blockade peaks by electronic correlations in InAs nanowires

We performed electronic transport measurements on 1D InAs quantum wires. In sufficiently disordered wires, transport is dominated by Coulomb blockade, and the conductance can be well described by tunneling through a quantum dot embedded between two one-dimensional Luttinger liquid wires. In contrast to previous experiments in other material systems, in our system the conductance difference between peak to valley decreases with decreasing temperature for several consecutive peaks. This phenomenon is theoretically expected to occur only for strongly interacting systems with small Luttinger interaction parameter g < 1/2; we find for our InAs wires a value of g~0.4. Possible mechanisms leading to these strong correlations are discussed.

Growth and kinetic Monte Carlo simulation of InAs quantum wires on vicinal substrates

Self-assembled quantum structures have been successfully grown for some time now but control over their uniformity has proven difficult due to the stochastic nature of surface diffusion. We have investigated the effect of vicinal InP(001) substrates on the uniformity of InAs quantum wires grown on InGaAlAs lattice-matched to InP using molecular beam epitaxy. Dense quantum wires were grown on both nominally flat and vicinal substrates off-cut by 0.9° toward the [110] direction for comparison. The off-cut angle was chosen to provide terraces which match the orientation and spacing of wires grown on nominally flat substrates. A modest but statistically significant improvement in the size distribution of the wires was observed on vicinal substrates through the analysis of ultrahigh resolution scanning electron micrographs. The interface between the wires and the off-cut substrate was studied using cross-sectional high resolution scanning transmission electron microscopy. In addition, a kinetic Monte Carlo model of epitaxial growth including full strain calculations was developed to further investigate the nucleation process. Using an anisotropic bond model to account for the surface energy of different crystallographic facets, our simulations produced wires similar to those observed experimentally while demonstrating the importance of anisotropic bonding compared to anisotropic diffusion. Growth on vicinal substrates is also simulated here and indicates that off-cut substrates should indeed improve the size distribution of quantum wires under proper growth conditions.

The electronic transport of top subband and disordered sea in an InAs nanowire in the presence of a mobile gate

We performed measurements at helium temperatures of the electronic transport in an InAs quantum wire (Rwire ∼ 30 kΩ) in the presence of a charged tip of an atomic force microscope serving as a mobile gate. The period and the amplitude of the observed quasi-periodic oscillations are investigated in detail as a function of electron concentration in the linear and non-linear regime. We demonstrate the influence of the tip-to-sample distance on the ability to locally affect the top subband electrons as well as the electrons in the disordered sea. Furthermore, we introduce a new method of detection of the subband occupation in an InAs wire, which allows us to evaluate the number of electrons in the conductive band of the wire.

Size Distribution, Imaging and Growth Mechanisms of Self-Assembled InAs Quantum Wires on Vicinal Substrates

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Distortions of the coulomb blockade conductance line in scanning gate measurements of inas nanowire based quantum dots

We performed measurements at helium temperatures of the electronic transport in the linear regime in an InAs quantum wire in the presence of a charged tip of an atomic force microscope (AFM) at low electron concentration. We show that at certain concentration of electrons, only two closely placed quantum dots, both in the Coulomb blockade regime, govern conductance of the whole wire. Under this condition, two types of peculiarities—wobbling and splitting—arise in the behavior of the lines of the conductance peaks of Coulomb blockade. These peculiarities are measured in quantum-wire-based structures for the first time. We explain both peculiarities as an interplay of the conductance of two quantum dots present in the wire. Detailed modeling of wobbling behavior made in the framework of the orthodox theory of Coulomb blockade demonstrates good agreement with the obtained experimental data.

Bonding to antibonding transition for hole ground states in coupled InAs quantum wires

We calculate hole energies of the bonding and antibonding states in coupled quantum wires using 6-band kp model. It is shown that hole ground state changes character from a bonding to an antibonding orbital with increasing inter-wire distances. This effect is a consequence of the enhancement of light hole contribution to the ground state. The variations of g factors under external electric and magnetic fields demonstrate the antibonding character of hole ground states.

Equal coupling strength approach to spin precession effects concerning Rashba and Dresselhaus spin–orbit interactions in the presence of in-plane magnetic fields

The influence of Rashba and Dresselhaus spin–orbit interactions on the electronic properties of quasi one-dimensional systems like InAs quantum wires is discussed in the presence of in-plane magnetic fields. One shows that equal coupling strength conditions are provided specifically by the commutativity of two-dimensional constituents of velocity and current operators. The interesting point is that equal strength spin–orbit couplings one deals with proceed in conjunction with related spin conservations, which amounts to account for selected orientations of the magnetic field. Accordingly, the in-plane magnetic fields should be directed solely along the bisectrices. Other angles may be conceivable, but in this case spin conservations alluded to above are lost. Such results open the way to a consistent derivation of the equal coupling strength limit of the energy, which leads in turn to the derivation of novel spin-precession effects. A related effective gyromagnetic factor has also been established.

Electron g-factor in quantum wire in the presence of Rashba effect and magnetic field

In this paper, we study the electron effective Landé g-factor in the InAs quantum wire under an applied magnetic field and the Rashba effect. For this goal, we first present an analytic solution to one-particle Schrödinger equation in the presence of both magnetic field and spin–orbit interaction (SOI). Then, using the obtained energy levels, we study the electron effective Landé g-factor. It is found that: (i) The effective Landé g-factor decreases when magnetic field increases. (ii) By increasing the confinement length l 0 , the electron g-factor decreases. (iii) By increasing the strength of SOI, the electron g-factor increases.

New method of creation of a rearrangeable local Coulomb potential profile and its application for investigations of local conductivity of InAs nanowires

We present a new technique to create a reconfigurable Coulomb potential profile. The potential profile on the sample surface covered with residual polymethyl methacrylate (PMMA) layer as charge accumulation substance is performed with a low DC voltage applied to conductive probe tip of scanning microscope. To characterize the resulted Coulomb potential profile Kelvin probe technique is used. The effectiveness of this method is demonstrated by performing measurements of the local conductivity of InAs quantum wires. These investigations revealed an inhomogeneous conductivity of the wires and the formation of a potential barrier in the wire at the contact pad interface when the electronic system of the wire is depleted.

Growth of InAs Quantum Wires with Ga-Assisted Deoxidation on Cleaved-Edge GaAs (110) Surface

We have fabricated site-controlled InAs quantum wires (QWRs) on the cleaved surface (110) of AlGaAs/GaAs superlattices (SLs) structures by using Ga-assisted deoxidation method. In the surface of SLs regions, InAs QWRs were nucleated on GaAs in stead of AlGaAs. In the (110) surface without superlattices(SLs) structures, QDs with a large size were obtained, which is considered hard to realize. To understand the different InAs growth phenomena in the regions with and without superlattices structures, we suggest that indium adatoms have an apparent trend to migrate to the SLs area.

Effect of layer separation, InAs thickness, and rapid thermal annealing on the optical emission from a multi-layer quantum wire structure

Multi-layer InAs quantum wire stacks with different layer separations (8, 15, and 25 nm) and InAs thicknesses (3, 4, 5, and 7 monolayers [ML]) were grown on and embedded in In0.53Ga0.27Al0.20As barrier/spacer layers lattice-matched to an InP substrate. For the samples with 4 ML of InAs and different layer separations, double peak photoluminescence was observed from quantum wire stacks separated by 8 nm, and with a 15 nm spacer layer a long wavelength component was observed extending from the main peak. Only a single peak was found as the spacer layer thickness was increased to 25 nm. For the quantum wire stacks with different InAs layer thicknesses and a separation of 8 nm, double peak photoluminescence spectra were observed in the sample with 4 ML of InAs, and a main peak with a long wavelength component was obtained from the sample with 3 ML of InAs. Only a single peak was detectable for the InAs layer thicknesses of 5 and 7 ML. The optical emission features were studied via temperature and excitation laser power dependent photoluminescence. Based on the photoluminescence and transmission electron microscopy observations, photoluminescence spectral features can be attributed to a bi-modal height distribution in certain samples. In order to extend the optical emission to room temperature, the sample with 5 ML of InAs and an 8 nm spacer layer was subjected to post-growth rapid thermal annealing at different temperatures. The emission wavelength was tunable from 1.63 to 1.72 μm at room temperature.

Circular photogalvanic effect induced by near-infrared radiation in InAs quantum wires patterned quasi-two-dimensional electron system

In this letter we investigated the InAs/InAlAs quantum wires (QWRs) superlattice by optically exciting the structure with near-infrared radiation. By varying the helicity of the radiation at room temperature we observed the circular photogalvanic effect related to the C2v symmetry of the structure, which could be attributed to the formation of a quasi-two-dimensional system underlying in the vicinity of the QWRs pattern. The ratio of Rashba and Dresselhaus terms shows an evolution of the spin–orbit interaction in quasi-two-dimensional structure with the QWR layer deposition thickness.

Polarization and Excitation Dependence of Photoluminescence of InAs Quantum Wires and Dots Grown on GaAs(631)

Polarization and Excitation Dependence of Photoluminescence of InAs Quantum Wires and Dots Grown on GaAs(631)

Polarization and Excitation Dependence of Photoluminescence of InAs Quantum Wires and Dots Grown on GaAs(631)

We studied the optical properties of self-assembled InAs nanostructures grown by molecular beam epitaxy on GaAs substrates with (631) crystallographic orientation by photoluminescence (PL) spectroscopy. The growth of InAs proceeded on GaAs(631) buffer layers conformed by corrugated surfaces with a high degree of lateral periodicity (uniformly spaced nano grooves). The grooved surface is sustained even after the growth of InAs with thicknesses below 2 monolayers (ML), indicating the formation of InAs quantum wires. The one-dimensional confinement is corroborated by PL polarized along the [113] and [8,19,9] orthogonal directions. The calculated polarization degree, Πd, was 0.13 and 0.125 for InAs thicknesses of 1 and 1.5 ML, respectively. As the InAs thickness is increased, the InAs film reaches the critical thickness and quantum dots aligned along the grooved surface are formed, as observed by atomic force microscopy. Excitation-power-dependent luminescence is observed to a larger extent for low-energy PL lines in addition to a blue shift related to the band-filling effect.

Anomalous Temperature Dependence of Photoluminescence in InAs/InAlGaAs/InP Quantum Wire and Dot Hybrid Nanostructures

Self-assembled InAs quantum wires (QWRs) are fabricated on an InP substrate by solid-source molecular beam epitaxy (SSMBE). Photoluminescence (PL) spectra are investigated in these nanostructures as a function of temperature. An anomalous enhancement of PL intensity and a temperature insensitive PL emission are observed from InAs nanostructures grown on InP substrates using InAlGaAs as the matrix layer and the origin of this phenomenon is discussed. We attribute the anomalous temperature dependence of photoluminescence to the formation of Al-rich and In-rich region in the InAlGaAs buffer layer and the cap layer.

InAs quantum wire induced composition modulation in an In0.53Ga0.37Al0.10As barrier layer grown on an InP substrate

Composition modulations are observed by transmission electron microscopy in In0.53Ga0.37Al0.10As barrier layers that overgrow both single- and multilayer InAs quantum wire structures grown on an InP substrate. Indium-rich (gallium-deficient) regions were observed in the region of the barrier layer lying directly above individual quantum wires, while indium-deficient (gallium-rich) regions were detected in the barrier above the gaps between adjacent underlying quantum wires. The magnitude of such modulation was typically 7% (atomic percent) for both indium and gallium as estimated from the energy dispersive x-ray analysis. The origin of such composition modulations was determined by modeling the chemical potential distribution for indium and gallium on the growth front of the barrier layer at the initial capping stage of the quantum wires with finite element simulations. It is found that the number and positions of the indium-rich regions are determined by the combined effects of strain and surface energy distributions on the barrier material capping the quantum wires. Moreover the estimated magnitudes of the composition modulation for both indium and gallium from the finite element models are in good agreement with the experimental observations. This method provides a simple way to understand the origin of, and to estimate the magnitude of the quantum wire-induced composition modulation in the barrier layer.

Stacking pattern of multi-layer InAs quantum wires embedded in In 0.53Ga 0.47− xAl xAs matrix layers grown lattice-matched on InP substrate

Multi-layer InAs quantum wires were grown on, and embedded in In 0.53Ga 0.47− x Al x As (with x=0, 0.1, 0.3 and 0.48) barrier/spacer layers lattice matched to an InP substrate. Correlated stacking of the quantum wire arrays were observed with aluminum content of 0 and 0.1. The quantum wire stacks became anti-correlated as the aluminum content was increased to 0.3 and 0.48. The origin of such stacking pattern variation was investigated by finite element calculations of the chemical potential distribution for indium on the growth front surface of the capping spacer layer. It is shown that the stacking pattern transition is determined by the combined effect of strain and surface morphology on the growth front of the spacer layers.