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In this paper, a scaling study of heterojunction solar cells based on p-type silicon quantum wires with rectangular cross sections in the sub-10-nm regime and graphene (p-SiQWs/G) is presented. The scaling issues in p-SiQWs/G solar cells performance focusing on SiQWs diameter, the distance between SiQWs, and the number of graphene layers is investigated by a coupled optical and electrical model taking into account the quantum effects of SiQWs. A minimum efficiency of p-SiQWs/G solar cells is obtained for SiQWs with moderate diameter. The p-SiQWs/G solar cell with small diameter shows high efficiency because of wide band gap of SiQWs with small diameter. On the other hand, p-SiQWs/G solar cell with large diameter also shows high efficiency because of strong light absorption of SiQWs resulted from high surface area. The results also show that the denser packing of SiQWs and monolayer graphene improve the efficiency of p-SiQWs/G solar cells. [ABSTRACT FROM AUTHOR]

The finite-difference and finite-element methods are employed to solve the one-dimensional single-band Schrödinger equation in the planar and cylindrical geometries. The analyzed geometries correspond to semiconductor quantum wells and cylindrical quantum wires. As a typical example, the GaAs/AlGaAs system is considered. The approximation of the lowest order is employed in the finite-difference method and linear shape functions are employed in the finite-element calculations. Deviations of the computed ground state electron energy in a rectangular quantum well of finite depth, and for the linear harmonic oscillator are determined as function of the grid size. For the planar geometry, the modified Pöschl-Teller potential is also considered. Even for small grids, having more than 20 points, the finite-element method is found to offer better accuracy than the finite-difference method. Furthermore, the energy levels are found to converge faster towards the accurate value when the finite-element method is employed for calculation. The optimal dimensions of the domain employed for solving the Schrödinger equation are determined as they vary with the grid size and the ground-state energy. [Projekat Ministarstva nauke Republike Srbije]

A quantum wire subjected to electric and step-like magnetic fields is numerically studied. Electron energy spectrum and eigenstates are calculated using effective mass approximation. We find an electric field causes crossing and anticrossing behaviours of energy spectrum which are associated with the occurrence of bonding and antibonding states. For ballistic transport, the electron conductance exhibits stepwise variation with some peaks and dips. The conductance character is interpreted by analyzing energy dispersion. [ABSTRACT FROM AUTHOR]

In this paper, we report a theoretical study of the optical properties of InAs/In 0.52 Al 0.48 As quantum wire subjected to an inclined transverse electric field. For this purpose, we have used the effective mass approximation. The energy levels and the wave function of the ground and the first excited states have been calculated for different values of the electric field. The intersubband transition energy, the oscillator strength and the optical absorption coefficient have been also investigated. Thus, the effect of the tilt angle and the intensity of the electric field on the optical properties of the quantum wire, along the width direction, have been examined. [ABSTRACT FROM AUTHOR]

In this work, we investigate GaSb / InAs 1 − x N x T-shaped quantum wire active region in mid-infrared laser. Multi-band k.p model and variational formalism are applied to find the confinement energies, the band structures, and optical gain. We then present a method of numerical calculation that is suited to any T-shaped quantum wire. By tuning the quantum wire thickness, the TE- and TM-polarized optical gain up to 21 × 10 3 cm − 1 can be obtained for λ = 3.11 μm at room temperature (RT), which is very promising to serve as an alternative active region for high-efficiency mid-infrared laser applications. [ABSTRACT FROM AUTHOR]

We report on possibility of charge current generation in nanowire made of two tunnel coupled one-dimensional electron waveguides by means of single magnetic pulse lasting up to 20 ps. Existence of interlayer tunnel coupling plays a crucial role in the effect described here as it allows for hybridization of the wave functions localized in different layers which can be dynamically modified by applying a time changeable in-plane magnetic field. Results of time-dependent DFT calculations performed for a bilayer nanowire confining many electrons show that the effect of such magnetic hybridization relies on tilting of electrons’ energy subbands, to the left or to the right, depending on a sign of time derivative of oscillating magnetic field due to the Faraday law. Consequently, the tilted subbands become a source of charge flow along the wire. Strength of such magneto-induced current oscillations may achieve even 0.6 μ A but it depends on duration of magnetic pulse as well as on charge density confined in nanowire which has to be unequally distributed between both transport layers to observe this effect. [ABSTRACT FROM AUTHOR]

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The hot-electron energy-loss rate via the acoustic-phonons in an embedded semiconductor quantum wire of circular cross section in the presence of external electric field has been investigated using deformation potential theory. Dimensional confinement effect on modifying acoustic-phonon modes are taken into account. The energy-loss rate as a function of electric field strength, electron density and electron temperature is obtained. Our calculations show that the electric field applied perpendicularly to the wire axis can be used as an important tool for the control of the energy-loss processes in nanowires. [ABSTRACT FROM AUTHOR]

We study the quantum tunneling of a two-level multi-crossing system in an accelerating one-dimensional optical parabolic potential manifested in a 3D heterostructure magnetic quantum wire. By direct integration using the Dynamic matrix approach (DMA), we establish the time and magnetic field dependencies of the generalized analytic expressions of the survival and transition probabilities, respectively in the presence and in the absence of a harmonic confinement potential. The system causes a modulation of the transition frequency which differs from the one observed in the Landau-Zener (LZ) theory that appear when such magnetic inhomogeneity occurs. It is shown that in the absence of a curved confinement and for exceedingly low and extremely high frequencies of the magnetic field, the phase difference of the two wave packets acquired between subsequent crossings allows us to probe Landau-Zener-Stückelberg (LZS) interferometry effects. Otherwise, in the presence of a curved confinement and for low values of the LZ parameter, the system readily exhibits more multi-crossings in the tunneling probabilities. The probe qubit spectrum obtained from this approach can be used to characterize the qubit evolution in the sample while the DMA is used for the modeling of dynamic spins in order to satisfy an optimum control quality with high accuracy. [ABSTRACT FROM AUTHOR]

The theory of rate of loss of energy of non-equilibrium electrons due to inelastic interaction with the intravalley acoustic phonons in a nano-dimensional semiconductor wire has been developed under the condition of low lattice temperature, when the approximations of the well known traditional theory are not valid. Numerical results are obtained for narrow-channel GaAs-GaAlAs wires structures. On comparison with other available results it is revealed that the finite energy of the intravalley acoustic phonons and, the use of the full form of the phonon distribution without truncation to the equipartition law, produce significant changes in the energy loss characteristics at low temperatures. [ABSTRACT FROM AUTHOR]

A quantum kinetic equation for electrons interacting with confined phonons is used to investigate the nonlinear absorption of an intense electromagnetic wave by electrons in cylindrical GaAs/AlAs quantum wires. The analytic expression for absorption coefficient is calculated for three models of confined optical phonons: the dielectric continuum (DC), hydrodynamic continuum (HC), and Huang-Zhu (HZ) models. The absorption coefficient depends on the square of the electromagnetic wave amplitude. The electrophonon resonance and optically detected electrophonon resonance (ODEPR) are observed through the absorption spectrum. The full width at half maximum (the line-width) of the ODEPR peaks is obtained by a computational method. The line-width is found to increase with increasing temperature and decrease with increasing the quantum wire radius. In particular, numerical results show that the DC and HZ models lead to a similar behaviour of electron - confined phonon interaction whereas the HC model results in a quite different one, especially at small quantum wire radius. For large quantum wire radii, above mentioned phonon models have equivalent contributions to the ODEPR line-width. [ABSTRACT FROM AUTHOR]

Electronic and optical properties of wurtzite (WZ) nonpoalr a-plane In x Ga 1 − x N/GaN quantum wire (QWR) structures are investigated as a function of the In content and the QWR size. In the c-plane, the spontaneous emission peak exhibits a slight dependence on the In content, while in the a-plane, the peak intensity significantly increases as the In content rises from 0.2 to 0.3. This is mainly due to the carrier confinement effect in QWRs with a higher In content. Spontaneous emission peaks of a-plane are shown to be much larger than those of c-plane irrespective of the In content, in particular, for x ≥ 0. 3. Also, the a-plane shows much larger peak intensity than the c-plane, irrespective of the QWR size. We expect that nonpolar a-plane QWRs are attractive for optoelectronic device applications with high internal efficiency. • We investigated optical properties of c- and a-plane wurtzite (WZ) InGaN/GaN quantum wires (QWRs). • The a-plane shows larger peak intensity than the c-plane, irrespective of the In content. • In particular, the peak intensities for a-plane are much larger than those for c-plane for x > = 0.3. • The a-plane shows much larger peak intensity than the c-plane, irrespective of the QWR size. • Nonpolar a-plane QWRs are attractive for optoelectronic devices with high internal efficiency. [ABSTRACT FROM AUTHOR]