Size Of Quantum Wires Research Articles

Thermodynamical properties of triangular quantum wires: entropy, specific heat, and internal energy

In the present work, thermodynamical properties of a GaAs quantum wire with equilateral triangle cross section are studied. First, the energy levels of the system are obtained by solving the Schrodinger equation. Second, the Tsallis formalism is applied to obtain entropy, internal energy, and specific heat of the system. We have found that the specific heat and entropy have certain physically meaningful values, which mean thermodynamic properties cannot take any continuous value, unlike classical thermodynamics in which they are considered as continuous quantities. Maximum of entropy increases with increasing the wire size. The specific heat is zero at special temperatures. Specific heat decreases with increasing temperature. There are several peaks in specific heat, and these are dependent on quantum wire size.

Electron spin relaxation in n-type InAs quantum wires

We investigate the electron spin relaxation of n-type InAs quantum wires by numerically solving the fully microscopic kinetic spin Bloch equations with the relevant scattering explicitly included. We find that the quantum-wire size and the growth direction influence the spin relaxation time by modulating the spin-orbit coupling. Due to intersubband scattering in connection with the spin-orbit interaction, spin-relaxation in quantum wires can show different characteristics from those in bulk or quantum wells and can be effectively manipulated by various means.

Hole spin relaxation inp-type GaAs quantum wires investigated by numerically solving fully microscopic kinetic spin Bloch equations

We investigate the spin relaxation of $p$-type GaAs quantum wires by numerically solving the fully microscopic kinetic spin Bloch equations. We find that the quantum-wire size influences the spin-relaxation time effectively by modulating the energy spectrum and the heavy-hole--light-hole mixing of wire states. The effects of quantum-wire size, temperature, hole density, and initial polarization are investigated in detail. We show that, depending on the situation, the spin-relaxation time can either increase or decrease with hole density. Due to the different subband structure and effects arising from spin-orbit coupling, many spin-relaxation properties are quite different from those of holes in the bulk or in quantum wells, and the intersubband scattering makes a marked contribution to the spin relaxation.

Comparison between Quantum Confinement Effects of Quantum Wires and Dots

Dimensionality is an important governing factor in the electronic structures of semiconductor nanocrystals. The quantum confinement energies in one-dimensional quantum wires and zero-dimensional quantum dots are quite different. Using large-scale first-principle calculations, we have systematically studied the electronic structures of semiconductor (including group IV, III−V, and II−VI materials) surface-passivated quantum wires and dots. We have found that the band-gap energies of quantum wires and dots have the same scaling with diameter for a given material. The ratios of band-gap increases between quantum wires and dots are material-dependent, and for most direct band-gap materials, this ratio is very close to 0.586, as predicted by simple effective-mass approximation. We also have found a highly linear polarization of photoluminescence in quantum wires. The degree of polarization decreases with the increasing temperature and quantum wire size.

Control of the crystallite size and passivation of defects in porous silicon by a novel method

Porous silicon films were prepared by lateral anodization of crystalline silicon in HF based solutions at different current densities. At an optimum current density, passivation of the defects by an appropriate post-anodization treatment results in the significant enhancement in the photoluminescence (PL) efficiency. However, above the optimum current level, a phase is obtained which shows significant broadening of the PL spectrum indicating the quantum wire size distribution. The degraded PL intensity in the treated samples is higher as compared to that for the as-anodized samples. Infrared vibrational studies indicate that this enhancement is due to the H-passivation of defects in the Si-pore interface, though the presence of hydrogen-terminated silicon clusters cannot be ignored. Capacitance–voltage studies concur well with the photoluminescence and infrared results.

Dynamic Transport of Interacting Electrons in a Mesoscopic Quantum Wire

Electron density distribution in a quantum wire (QW) coupledto reservoirs is investigated, treating this structure as aunified quantum system and taking into account the Coulombinteraction of electrons. We show that electrons aretransferred between the QW and the reservoirs when theequilibrium state is established. As a result the QWacquires a positive or negative charge or remains neutral as awhole, depending on the QW size and the background charge.Electron transport in a QW is investigated for the lattercase using the model which allows one to treat exactly theCoulomb interaction. We study the Coulomb interaction effecton the dynamic conductance. The real part of the impedanceshows a resonant behavior versus the frequency which is causedby the reflection of the charge waves from the contacts andtheir interference in the QW. The Coulomb interaction effectconsists in a nonlinear dependence of the resonant frequencieson the wave number. No effective interaction parameter of theLuttinger liquid can simulate the frequency dependence of theimpedance calculated with the real Coulomb interaction.

Low-dimensional electron transport properties in InAs/AlGaSb mesoscopic structures

We report on the successful fabrication and electrical transport properties of single quantum wires fabricated by using InAs/AlGaSb heterostructures. Magnetotransport and high electric field characteristics have been measured on the various size of quantum wires. From comparison with the channel length-dependence of I–V characteristics of the different size quantum wires, we try to develop a comprehensive understanding on the quasi-one dimensional electron transport in InAs from the nearly ballistic regime to the hot electron condition. The fabrication and characteristics of superconducting weak link InAs/Pb:In devices are also reported. The modulation of differential conductivity has been observed by the gate bias voltage between the superconducting Pb–In contacts.

Low threshold current density operation of GaInP-AlGaInP visible multiple quantum wire-like lasers (MQWR-LDs) under the room temperature pulsed condition

GaInP-AlGaInP multiple quantum wire-like layers were fabricated by the in situ strain induced lateral layer ordering process during MBE growth. According to TEM images, the quantum wire size was around 10 nm and quantum wire axis was along [011~] direction. When we made laser diodes with stripes along [011] direction, the low threshold current density, of 315 A/cm/sup 2/ was obtained. Anisotropic lasing characteristics between [011] and [011~] directions, in threshold current density, lasing mode, and lasing wavelength were observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Room-temperature operation of GaInAs/GaInAsP/InP SCH lasers with quantum-wire size active region

Improvements in the fabrication of GaInAs(P)/InP devices consisting of an ultrafine structure by using two-step organometallic vapor phase epitaxy (OMVPE) growth, electron beam exposure direct writing, and wet chemical etching are reported. This improved process achieved, for the first time, a room-temperature continuous-wave (CW) operation of GaInAs/InP quantum-wire lasers consisting of 5-nm-thick and 10-30-nm-wide vertically stacked triple quantum-wire active region within the period of 70 nm. A large blue shift of approximately 40 nm was observed in both the lasing and the electroluminescence spectra of Ga/sub 0.3/In/sub 0.7/As/InP compressively strained multi-quantum-well (MQW) wire lasers consisting of a 3-nm-thick and 30-60-nm-wide five-wire active region, which suggests a reduced effective mass of holes along the in-plane direction. >

Gain spectra of quantum wires with inhomogeneous broadening

The effects of fabricational variations on the gain spectra of quantum wires are calculated within the limits of first-order perturbation theory. Gain spectra and density of states for 50-AA-radius and 150-AA-radius cylindrical quantum wires are calculated and plotted for several different fabrication tolerances. The wave functions for a finite, cylindrical potential are calculated and a quasicritical radius, below which the carriers are weakly confined by the potential, is established. This sets a lower limit on quantum wire size. Upper limits on the size of quantum wells, quantum wires, and quantum boxes are also discussed. The threshold current and differential gain of quantum-wire lasers and quantum wire array lasers are calculated. These calculations indicate a possible reduction in threshold current of one to two orders of magnitude as compared to the best quantum-well lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>