Semiempirical supercell approach to calculate the electronic and optical properties of Si quantum wires

Facta universitatis - series: Electronics and Energetics, 2015

The application of the Thomas-Fermi method to calculate the electron spectrum in quantum wells formed by highly doped n-Si quantum wires is presented under finite temperatures where the many-body effects, like exchange, are taken into account. The electron potential energy is calculated initially from a single equation. Then the electron energy sub-levels and the wave functions within the potential well are simulated from the Schr?dinger equation. For axially symmetric wave functions the shooting method has been used. Two methods have been applied to solve the Schr?dinger equation in the case of the anisotropic effective electron mass, the variation method and the iteration procedure for the eigenvectors of the Hamiltonian matrix.

Journal of Materials Science: Materials in Electronics, 2009

The photoluminescence lifetimes of Si quantum wires and dots have been previously calculated within a continuum model that takes into account the anisotropy of silicon band structure. Here, we present our calculations on the optical transitions in Si quantum wires modulated by a quantum dot. The geometrical parameters of the buldged wire are appropriate for porous Si and the ground state is localized. The photoluminescence lifetimes are calculated and compared with those of straight wires and dots. The magnitude of the lifetime is sensitive to the structural parameters of the nanostructures. Lifetimes varying from nanoseconds to milliseconds have been obtained. The results of the calculations provide insight to the optical properties of Si nanostructures.

Physica Status Solidi B-basic Solid State Physics, 2010

The study of semiconducting nanowires is one of the most rapidly growing research areas in materials science and nanotechnology, not only from the point of view of the possible applications, but also regarding the use of the latest developments in the theory. In this paper, we review the general ab initio many-body theory and methods and resume some of our very recent results regarding the structural, electronic, and optical properties of Silicon nanowires (Si-NWs), outlining both the reached achievements and some of the technical aspects necessary to obtain them.

The optical reflectivity and transmission in semiconductor quantum wire grating, are considered theoretically for an incidence parallel to the layers. The curves are obviousness in favour of coupled TE and TM band gap energy with very high reflectivity for θ > 80? and which is accompanied by a nearly vanishing transmittance. In such an extended energy range, the system behaves as a mirror.

physica status solidi (b), 2010

The study of semiconducting nanowires is one of the most rapidly growing research areas in materials science and nanotechnology, not only from the point of view of the possible applications, but also regarding the use of the latest developments in the theory. In this paper, we review the general ab initio many-body theory and methods and resume some of our very recent results regarding the structural, electronic, and optical properties of Silicon nanowires (Si-NWs), outlining both the reached achievements and some of the technical aspects necessary to obtain them.

physica status solidi (a), 2000

Calculations of the binding energy of excitons are carried out for silicon quantum wires embedded in a dielectric ambient. The calculations showed a decrease of the Bohr radius and an increase of the binding energy with decreasing wire diameter. Photoluminescence measurements performed on PS samples filled with different organic media showed good agreement with theory.

Computer Methods in Applied Mechanics and Engineering, 2000

This paper introduces the main numerical issues related to the simulation of electronic states in highly con®ned semiconductor systems. A typical example is the semiconductor quantum wire, where double size quantization con®nes carriers on the cross-section of a conduction channel. We introduce details of the numerical approach for the solution of the coupled Poisson/Schr odinger equation system that describe the quantum system and outline an original iteration approach that uses a predictor±corrector procedure for convergence of the outer iteration. The numerical approach is illustrated by a number of examples for quantum wire structures based on the GaAs/AlGaAs and the Si/SiO 2 material systems. The simulations for Si-based structures are interesting to understand the limit of scalability of traditional integrated devices in the plane transverse to the conduction channel. It is also shown that a quasi± monomode Si quantum wire is in principle possible at room temperature.

Physical Review B, 2002

The low-energy properties of a homogeneous one-dimensional electron system are completely specified by two Tomonaga-Luttinger parameters K and v . In this paper we discuss microscopic estimates of the values of these parameters in semiconductor quantum wires that exploit their relationship to thermodynamic properties. Motivated by the recognized similarity between correlations in the ground state of a one-dimensional electron liquid and correlations in a Wigner crystal, we evaluate these thermodynamic quantities in a selfconsistent Hartree-Fock approximation. According to our calculations, the Hartree-Fock approximation ground state is a Wigner crystal at all electron densities and has antiferromagnetic order that gradually evolves from spin-density wave to localized in character as the density is lowered. Our results for K are in good agreement with weak-coupling perturbative estimates K pert at high densities, but deviate strongly at low densities, especially when the electron-electron interaction is screened at long distances. K pert ϳn 1/2 vanishes at small carrier density n, whereas we conjecture that K →1/2 when n→0, implying that K should pass through a minimum at an intermediate density. Observation of this nonmonotonic dependence could be used to measure the effective interaction range in a realistic semiconductor quantum wire geometry. In the spin sector we find that the spin velocity decreases with increasing interaction strength or decreasing n. Strong correlation effects make it difficult to obtain fully consistent estimates of v from Hartree-Fock calculations. We conjecture that v /v F ϰn/V 0 , where V 0 is the interaction strength, in the limit n→0.

We have used an efficient method based on the coordinate transformation for numerical modeling of different shapes of quantum wires. a b s t r a c t In this work, we propose an efficient method to investigate optical properties as well as their dependence on geometrical parameters in InAs/InAlAs quantum wires. The used method is based on the coordinate transformation and the finite difference method. It provides sufficient accuracy, stability and flexibility with respect to the size and shape of the quantum wire. The electron and hole energy levels as well as their corresponding wave functions are investigated for different shape of quantum wires. The optical transition energies, the emission wavelengths and the oscillator strengths are also studied.

Journal of Applied Physics, 2006

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Physical Review B, 2005

We have studied corrugated quantum wells as a semiconductor quantum wire structure. The quantum well corrugation results from a step bunching effect during epitaxial growth on vicinal ͑111͒ GaAs substrates and might be used to form a quantum wire superlattice. The strain and piezoelectric effects were studied both by an atomistic valence force field method and by an elastic continuum model. Within the elastic continuum model we also studied the electromechanical coupling. The electronic band structure was calculated with the eightband k•p model. The nonphysical oscillating solutions were eliminated by appropriate fine tuning of the material parameters. We have also studied the density of states and the polarization dependence of interband light absorption in the electric dipole approximation.

Moldavian Academy of Sciences, Institute of Applied Physics, Laboratory of Physical Kinetics (Academic Str. 5, MD-2028, Kishinev) The defense will take place on December 18, 2002 at 2 p.m. in the framework of the meeting of the specialized Scientific Council .16 at the State University of Moldova (Mateevici Str. 60, MD-2009, Kishinev) The Ph.D. thesis and the abstract can be consulted at the library of the State University of Moldova, Mateevici Str. 60, Kishinev The abstract was mailed on November 14, 2002 Scientific Secretary of the specialized Scientific Council, Doctor of Physical and Mathematical Sciences V. Pleşca 3

Thin Solid Films, 2000

A new device based on side-gated wires demonstrates that the side gate wire technique can be successfully implemented as a novel selective depletion scheme for vertical tunneling devices. Resonant tunneling between 1D states was achieved by an additional lateral con®nement generated by a central gate. From model considerations assuming a parabolic con®nement, the tuning range of the subband energy was estimated to lie between 0 meV and 5±6 meV. The transmittance of strongly coupled superlattices at different superlattice bias conditions is measured by varying the energy of the injected hot electron beam. The onset of scattering-induced miniband transport is clearly evident and the transition between coherent and incoherent electron transport in superlattices is observed for the ®rst time. A coherence length of 150 nm and a scattering time of 1 ps is determined. The experimental result is in good agreement to a fully three-dimensional calculation including interface roughness with typical island sizes of 10 nm. This clearly demonstrates that interface roughness scattering limits the coherence length of ballistic electrons in the superlattice.

2003

In the last few years, many research groups have been trying to develop electroluminescent devices based on silicon. In particular, it has been shown that low-dimensional structures, such as silicon clusters, quantum wires and quantum wells, are suitable for this purpose. In this work we investigate transport properties of a particular superlattice using two approaches. The first method is a Monte Carlo simulation of electron transport in the biased superlattice. The band structure is calculated using the envelope function approximation, and the scattering mechanisms introduced in the simulator are confined optical phonons. Owing to the particularly flat band structure, drift velocities are very low, but it will be shown that a parallel component of the electric field can significantly increase the vertical drift velocity. Moreover, a superlattice based device is proposed in order to obtain high recombination efficiency. Finally, a quantum calculation is introduced, in order to describe with higher accuracy the high field transport regime.